Adjust Github action workflow config to run only for master branch.

.github/workflows/test.yml

@@ -1,6 +1,12 @@
 name: Tests
 
-on: [push, pull_request]
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
 
 jobs:
   test: