ci: remove unused actions

These trigger dependency updates otherwise, which we don't need here.

.github/actions/artifact-from-cirrus/action.yaml

@@ -1,119 +0,0 @@
-name: Artifact from Cirrus
-
-description: Waits for a specific Cirrus CI run to complete, then downloads the artifact and uploads it to the current workflow. This will silently succeed if Cirrus CI did not schedule a task within 2 minutes.
-
-inputs:
-  download:
-    description: Name of Artifact to download from Cirrus CI
-    required: true
-  task:
-    description: Name of Cirrus Task
-    required: true
-  token:
-    description: GitHub Token
-    required: true
-  upload:
-    description: Name of Artifact to upload on GitHub Actions
-    required: true
-
-runs:
-  using: composite
-  steps:
-    - shell: bash
-      run: echo "GH_TOKEN=${{ inputs.token }}" >> "$GITHUB_ENV"
-    - name: Wait for Check Suite to be created
-      id: check-suite
-      env:
-        # GITHUB_SHA does weird things for pull request, so we roll our own:
-        COMMIT: ${{ github.event.pull_request.head.sha || github.sha }}
-      shell: bash
-      run: |
-        get_check_runs_url() {
-          gh api "repos/{owner}/{repo}/commits/${COMMIT}/check-suites" \
-            | jq -r '.check_suites[] | select(.app.slug == "cirrus-ci") | .check_runs_url'
-        }
-        for _ in $(seq 1 12); do
-          check_runs_url="$(get_check_runs_url)"
-          if [ -z "$check_runs_url" ]; then
-            echo "Cirrus CI task has not started, yet. Waiting..."
-            sleep 10
-          else
-            echo "check_runs_url=$check_runs_url" >> "$GITHUB_OUTPUT"
-            exit 0
-          fi
-        done
-        >&2 echo "Cirrus CI check suite not found. Is Cirrus CI enabled for this repo?"
-    - name: Find task by name
-      id: find-task
-      if: steps.check-suite.outputs.check_runs_url
-      shell: bash
-      run: |
-        get_number_of_tasks() {
-          gh api "${{ steps.check-suite.outputs.check_runs_url }}" \
-            | jq -r '.check_runs | map(select(.name == "${{ inputs.task }}")) | length'
-        }
-        tasks="$(get_number_of_tasks)"
-        case "$tasks" in
-          0)
-            echo "Task not found, assuming it's skipped intentionally..."
-            exit 0
-            ;;
-          1)
-            echo "task_found=1" >> "$GITHUB_OUTPUT"
-            exit 0
-            ;;
-          *)
-            >&2 echo "More than 1 task with the same name found. Don't know what to do..."
-            exit 1
-            ;;
-        esac
-    - name: Wait for Cirrus CI to complete task
-      if: steps.find-task.outputs.task_found
-      shell: bash
-      run: |
-        get_conclusion() {
-          gh api "${{ steps.check-suite.outputs.check_runs_url }}" \
-            | jq -r '.check_runs[] | select(.name == "${{ inputs.task }}" and .status == "completed") | .conclusion'
-        }
-        while true; do
-          conclusion="$(get_conclusion)"
-          if [ -z "$conclusion" ]; then
-            echo "Cirrus CI task has not completed, yet. Waiting..."
-            sleep 30
-          else
-            if [ "$conclusion" == "success" ]; then
-              break
-            else
-              exit 1
-            fi
-          fi
-        done
-    - name: Download artifact from Cirrus CI
-      if: steps.find-task.outputs.task_found
-      id: download
-      shell: bash
-      run: |
-        get_external_id() {
-          gh api "${{ steps.check-suite.outputs.check_runs_url }}" \
-            | jq -er '.check_runs[] | select(.name == "${{ inputs.task }}") | .external_id'
-        }
-        archive="$(mktemp)"
-        artifacts="$(mktemp -d)"
-        until curl --no-progress-meter --fail -o "${archive}" \
-                "https://api.cirrus-ci.com/v1/artifact/task/$(get_external_id)/${{ inputs.download }}.zip"
-        do
-          # This happens when a tag is pushed on the same commit. In this case the
-          # job is immediately marked as "completed" for us, so we end up here after a few
-          # seconds - but the actual Cirrus CI task is still running and didn't produce its artifact, yet.
-          echo "Artifact not found on Cirrus CI, yet. Waiting..."
-          sleep 30
-        done
-        unzip "${archive}" -d "${artifacts}"
-        echo "artifacts=${artifacts}" >> "$GITHUB_OUTPUT"
-    - name: Save artifact to GitHub Actions
-      if: steps.find-task.outputs.task_found
-      uses: actions/upload-artifact@b7c566a772e6b6bfb58ed0dc250532a479d7789f # v6.0.0
-      with:
-        name: ${{ inputs.upload }}
-        path: ${{ steps.download.outputs.artifacts }}
-        if-no-files-found: error

.github/actions/cache-on-main/action.yaml

@@ -1,35 +0,0 @@
-name: Cache on main
-
-description: Stores caches on main and release branches only, but restores them on all branches.
-
-inputs:
-  path:
-    description: Path(s) to cache
-    required: true
-  save-prs:
-    description: Whether to additionally store the cache in a pull request, too. Should only be used for very small caches.
-    type: boolean
-  prefix:
-    description: Cache key prefix to be used in both primary key and restore-keys.
-    required: true
-  suffix:
-    description: Cache key suffix to be used only in primary key.
-    required: true
-
-runs:
-  using: composite
-  steps:
-    - uses: actions/cache@9255dc7a253b0ccc959486e2bca901246202afeb # v5.0.1
-      if: ${{ startsWith(github.ref, 'refs/heads/') || (inputs.save-prs && startsWith(github.ref, 'refs/pull/')) }}
-      with:
-        path: ${{ inputs.path }}
-        key: ${{ runner.os }}-${{ inputs.prefix }}-${{ inputs.suffix }}
-        restore-keys: |
-          ${{ runner.os }}-${{ inputs.prefix }}-
-    - uses: actions/cache/restore@9255dc7a253b0ccc959486e2bca901246202afeb # v5.0.1
-      if: ${{ !startsWith(github.ref, 'refs/heads/') && !(inputs.save-prs && startsWith(github.ref, 'refs/pull/'))  }}
-      with:
-        path: ${{ inputs.path }}
-        key: ${{ runner.os }}-${{ inputs.prefix }}-${{ inputs.suffix }}
-        restore-keys: |
-          ${{ runner.os }}-${{ inputs.prefix }}-