ci: Be explicit about the version of linux and windows runner images

Using the -latest tag is potentially prone to errors, because an update of the tag
could break our CI. This recently happend with macos-latest, which we downgraded
to macos-12 earlier.

Using an explicit version reference makes this problem much less likely - in fact
renovate will pick up new versions once they exist and will suggest updates for it.
Thus, we will see the failures in a related PR instead of randomly everywhere.

.github/workflows/report.yaml

@@ -15,7 +15,7 @@ jobs:
     name: Loadtest
     permissions:
       checks: write
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     if: github.event.workflow_run.conclusion == 'success' || github.event.workflow_run.conclusion == 'failure'
     steps:
       - name: Download from Artifacts