ci(verifier): also tag and push :latest on release (#723)

the verifier release workflow only pushed the version tag, so
dstacktee/dstack-verifier:latest was stale (stuck at 0.5.4). add :latest
to the pushed tags so every release keeps it current.

Author: kvinwang

.github/workflows/verifier-release.yml

@@ -51,7 +51,9 @@ jobs:
           context: verifier
           file: verifier/builder/Dockerfile
           push: true
-          tags: ${{ vars.DOCKERHUB_ORG }}/dstack-verifier:${{ env.VERSION }}
+          tags: |
+            ${{ vars.DOCKERHUB_ORG }}/dstack-verifier:${{ env.VERSION }}
+            ${{ vars.DOCKERHUB_ORG }}/dstack-verifier:latest
           platforms: linux/amd64
           provenance: false
           build-contexts: |