workflows: bump vlaurin/action-ghcr-prune from 0.5.0 to 0.6.0

Bumps [vlaurin/action-ghcr-prune](https://github.com/vlaurin/action-ghcr-prune) from 0.5.0 to 0.6.0.
- [Release notes](https://github.com/vlaurin/action-ghcr-prune/releases)
- [Commits](vlaurin/action-ghcr-prune@v0.5.0...v0.6.0)

---
updated-dependencies:
- dependency-name: vlaurin/action-ghcr-prune
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

.github/workflows/pr-closed-docker.yaml

@@ -12,7 +12,7 @@ jobs:
       # We may need a specific token here with `packages:admin` privileges which is not available to GITHUB_TOKEN
       packages: write
     steps:
-      - uses: vlaurin/action-ghcr-prune@v0.5.0
+      - uses: vlaurin/action-ghcr-prune@v0.6.0
         with:
           organization: fluent
           container: fluent-bit/pr-${{ github.event.number }}