[#601] Delete untagged SNAPSHOT images

Author: chang-annie

.github/workflows/prune.yml

@@ -25,4 +25,6 @@ jobs:
           token: ${{ secrets.GHCR_IO_TOKEN }}
           exclude-tags: "^\\d+\\.\\d+\\.\\d+$"
           use-regex: true
-          keep-n-tagged: 2
+          keep-n-tagged: 2
+          dry-run: true
+          delete-untagged: true