Perform more Tests on PHP 8.1

Signed-off-by: Lukas Kämmerling <lukas.kaemmerling@hetzner-cloud.de>

Author: LKaemmerling

.github/workflows/blackbox.yml

@@ -22,7 +22,7 @@ jobs:
       - name: Setup PHP
         uses: shivammathur/setup-php@v2
         with:
-          php-version: 7.4
+          php-version: 8.1
           coverage: none
 
       - name: Install dependencies

.github/workflows/checks.yml

@@ -22,7 +22,7 @@ jobs:
       - name: Setup PHP
         uses: shivammathur/setup-php@v2
         with:
-          php-version: 7.4
+          php-version: 8.1
           coverage: none
 
       - name: Install dependencies