fix test matrix

Author: Gummibeer

.github/workflows/run-tests.yml

@@ -14,7 +14,7 @@ jobs:
     strategy:
       fail-fast: true
       matrix:
-        php: [8.0, 8.1]
+        php: [8.0]
         laravel: [8.*, 9.*]
         dependency-version: [prefer-lowest, prefer-stable]
         os: [ubuntu-latest]