CI: Simplify 'on' definition

Author: okurz

.github/workflows/ci-tests.yaml

@@ -1,11 +1,5 @@
 name: Unit and integration tests
-on:
-  push:
-    branches:
-      - '*'
-  pull_request:
-    branches:
-      - '*'
+on: [push, pull_request]
 jobs:
   build:
     runs-on: ${{ matrix.os }}