fix: correct docker metadata tagging

Author: zx900930

.github/workflows/docker-image.yml

@@ -35,10 +35,9 @@ jobs:
         images: |
           triatk/univpn
         # Docker tags based on the following events/attributes
-        flavor: |
-          latest=${{ github.ref == 'refs/heads/main' }}
-          nightly=${{ github.ref != 'refs/heads/main' }}
         tags: |
+          type=raw,value=latest,enable=${{ github.ref == 'refs/heads/main' }}
+          type=raw,value=nightly,enable=${{ github.ref != 'refs/heads/main' }}
           type=schedule
           type=ref,event=branch
           type=ref,event=pr