chore(ci): allow tests to run on Pull Requests

Currently pull requests from forks don't trigger the test suite.

This allows the test suite to run on pull requests from forks after
manual approval by a codeowner.

Author: nvloff-f3

.github/workflows/ci.yaml

@@ -1,4 +1,8 @@
-on: [push]
+on:
+  push:
+    branches: [ "master"]
+  pull_request:
+    branches: [ "master"]
 permissions:
   contents: read
 jobs: