ci: use PHP 8.1 only

Author: owenvoke

.github/workflows/main.yml

@@ -10,7 +10,7 @@ jobs:
     name: Pest ${{ matrix.test-suite }} on PHP ${{ matrix.php }}
     strategy:
       matrix:
-        php: ["8.0", "8.1"]
+        php: [8.1]
         test-suite: ['phpcsfixer', 'phpstan', 'rector']
 
     steps: