.github: scope artifact to current app to avoid upload races

All container push jobs shared the same artifact namespace and each
downloaded every other container's artifacts with `artifact-*`, causing
parallel release uploads to collide with "already_exists" errors.

Narrow the pattern to `artifact-${{ inputs.app }}-*` so each push job
only handles its own amd64/arm64 pair.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

Author: troglobit

.github/workflows/build-push.yml

@@ -78,7 +78,7 @@ jobs:
     steps:
       - uses: actions/download-artifact@v4
         with:
-          pattern: artifact-*
+          pattern: artifact-${{ inputs.app }}-*
           merge-multiple: true
       - name: Artifact Variables
         id: vars