chore: fix cosign

Author: dploeger

.github/workflows/docker-publish.yml

@@ -34,7 +34,7 @@ jobs:
       # https://github.com/sigstore/cosign-installer
       - name: Install cosign
         if: github.event_name != 'pull_request'
-        uses: sigstore/cosign-installer@2.8.1
+        uses: sigstore/cosign-installer@v2.8.1
 
       # Workaround: https://github.com/docker/build-push-action/issues/461
       - name: Setup Docker buildx