upgrade docker/metadata-action to v4

.github/workflows/release-rc.yml

@@ -22,7 +22,7 @@ jobs:
 
     - name: Docker meta
       id: meta
-      uses: docker/metadata-action@v3
+      uses: docker/metadata-action@v4
       with:
         # images: weseek/growi,ghcr.io/weseek/growi
         images: ghcr.io/weseek/growi

.github/workflows/release-slackbot-proxy.yml

@@ -24,7 +24,7 @@ jobs:
 
     - name: Docker meta
       id: meta
-      uses: docker/metadata-action@v3
+      uses: docker/metadata-action@v4
       with:
         images: weseek/growi-slackbot-proxy,ghcr.io/weseek/growi-slackbot-proxy,asia.gcr.io/${{ secrets.GCP_PRJ_ID_SLACKBOT_PROXY }}/growi-slackbot-proxy
         tags: |