chore(ci): only tag Docker image with SHA

we're moving away from using the branch-based tags and
associated webhooks, so we won't need this image tag

.github/workflows/deploy.yml

@@ -61,6 +61,4 @@ jobs:
           context: .
           file: appcontainer/Dockerfile
           push: true
-          tags: |
-            ghcr.io/${{ github.repository }}:${{ github.ref_name }}
-            ghcr.io/${{ github.repository }}:${{ github.sha }}
+          tags: ghcr.io/${{ github.repository }}:${{ github.sha }}