github-ci: don't deploy tarballs per push

Follows up #6185

.github/workflows/source.yml

@@ -11,12 +11,8 @@ env:
 
 jobs:
   source:
-    # We want to run only on release branches and tags.
-    if: ( github.ref == 'refs/heads/master' ||
-        github.ref == 'refs/heads/1.10' ||
-        startsWith(github.ref, 'refs/heads/2.') ||
-        startsWith(github.ref, 'refs/tags') ) &&
-        ! endsWith(github.ref, '-notest')
+    # We want to run only on tags.
+    if: startsWith(github.ref, 'refs/tags/')
 
     runs-on: ubuntu-18.04