workflows: fix version (#5570)

Signed-off-by: Patrick Stephens <[email protected]>

Author: Pat

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

@@ -9,9 +9,10 @@ jobs:
     name: PR - cleanup pr-${{ github.event.number }} images
     runs-on: ubuntu-latest
     permissions:
+      # We may need a specific token here with `packages:admin` privileges which is not available to GITHUB_TOKEN
       packages: write
     steps:
-      - uses: vlaurin/action-ghcr-prune@0.4.0
+      - uses: vlaurin/action-ghcr-prune@v0.4.0
         with:
           organization: fluent
           container: fluent-bit/pr-${{ github.event.number }}