ci: Refactor get_cirrusci_freebsd script to GitHub action

This should make it more reliable and also easier to re-use, if we need
to.

Resolves #2555

.cirrus.yml

@@ -2,23 +2,16 @@ freebsd_instance:
   image_family: freebsd-14-0
 
 build_task:
+  # Don't change this name without adjusting .github/workflows/build.yaml
   name: Build FreeBSD (Stack)
   install_script: pkg install -y postgresql16-client hs-stack git
 
-  # This also includes nix and cabal related files, because the
-  # Github Actions build workflow will run on those and the
-  # "Fetch from FreeBSD" job should not fail.
   only_if: |
     $CIRRUS_TAG != '' || $CIRRUS_BRANCH == 'main' || $CIRRUS_BRANCH =~ 'v*' ||
     changesInclude(
       '.github/workflows/build.yaml',
-      '.github/actions/setup-nix/**',
-      '.github/scripts/**',
-      '.github/*',
-      '*.nix',
-      'nix/**',
+      '.github/actions/artifact-from-cirrus/**',
       '.cirrus.yml',
-      'cabal.project*',
       'postgrest.cabal',
       'stack.yaml*',
       '**.hs'