Add PHP 8.1 to test matrix

Author: ksassnowski

.github/workflows/run_tests.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        php: [8.0]
+        php: [8.0, 8.1]
         laravel: [8.*]
         dependency-version: [prefer-lowest, prefer-stable]
         include:
@@ -39,4 +39,4 @@ jobs:
           composer update --${{ matrix.dependency-version }} --prefer-dist --no-interaction
 
       - name: Execute tests
-        run: vendor/bin/phpunit
+        run: vendor/bin/phpunit