another try to fix when github actions run

The attempt in 7bbf38eeb4 to not run
checks twice for our own internal pull requests seem not to have worked,
because checks in external PRs were no longer executed.

This is another approach to achieve the same based on code found at
764f121f9a/.github/workflows/build-and-test.yml (L10-L12)

.github/workflows/phpCS.yml

@@ -1,15 +1,12 @@
 name: PHP Code Style
 
-on:
-    push:
-    pull_request:
-        branches:
-        - '**:**'
+on: [push, pull_request]
 
 jobs:
     phpcs:
         name: PHP CodeSniffer
         runs-on: ubuntu-latest
+        if: github.event_name == 'push' || github.event.pull_request.head.repo.full_name != github.repository
         steps:
             - uses: actions/checkout@v2
 

.github/workflows/testLinux.yml

@@ -1,15 +1,12 @@
 name: Linux Unit Tests
 
-on:
-    push:
-    pull_request:
-        branches:
-            - '**:**'
+on: [push, pull_request]
 
 jobs:
     run:
         name: PHP ${{ matrix.php-versions }}
         runs-on: ubuntu-latest
+        if: github.event_name == 'push' || github.event.pull_request.head.repo.full_name != github.repository
 
         strategy:
             matrix:

.github/workflows/testWindows.yml

@@ -1,15 +1,12 @@
 name: Windows Unit Tests
 
-on:
-    push:
-    pull_request:
-        branches:
-            - '**:**'
+on: [push, pull_request]
 
 jobs:
     run:
         name: PHP ${{ matrix.php-versions }}
         runs-on: windows-latest
+        if: github.event_name == 'push' || github.event.pull_request.head.repo.full_name != github.repository
 
         strategy:
             matrix: