fix(ci): Only generate SHA tags for branch pushes, not releases

Fixes Docker publish workflow failing on release events with invalid
tag format ':-{sha}' when {{branch}} template is empty.

Author: chris-freeman-glean

.github/workflows/publish-docker.yml

@@ -44,7 +44,7 @@ jobs:
             type=semver,pattern={{version}}
             type=semver,pattern={{major}}.{{minor}}
             type=ref,event=branch
-            type=sha,prefix={{branch}}-
+            type=sha,prefix=,enable=${{ github.event_name == 'push' && github.ref_type == 'branch' }}
             type=raw,value=latest,enable={{is_default_branch}}
           labels: |
             org.opencontainers.image.title=Glean MCP Server