chore: modernize github actions

Signed-off-by: Matthieu Gallien <matthieu.gallien@nextcloud.com>

Author: mgallien

.github/workflows/phpunit.yml

@@ -22,14 +22,14 @@ jobs:
 
     steps:
       - name: Set up php ${{ matrix.php-versions }}
-        uses: shivammathur/setup-php@v2
+        uses: shivammathur/setup-php@44454db4f0199b8b9685a5d763dc37cbf79108e1 # v2.36.0
         with:
           php-version: ${{ matrix.php-versions }}
           extensions: mbstring, iconv, fileinfo, intl
           coverage: none
 
       - name: Checkout server
-        uses: actions/checkout@v2
+        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
 
       - name: Run unit tests
         run: |