Remove the extra branch allowance. (#609)

This shouldn't be needed now that we've landed the new CI on trunk.

.github/workflows/tests.yaml

@@ -6,7 +6,7 @@ name: test
 
 on:
   push:
-    branches: [trunk, build-scaling]
+    branches: [trunk]
     paths:
       # Conservatively run the tests. However, skip them if the only paths in
       # the pull request match files that we know don't impact the build.