Narrow down test running on branches.

If we do a quick fix we want to avoid running both PR and push test on
$user-patchX.

.github/workflows/test.yml

@@ -2,6 +2,10 b' name: Run tests'
 
 on:
   push:
+    branches:
+      - main
+      - master
+      - '*.x'
   pull_request:
   # Run weekly on Monday at 1:23 UTC
   schedule: