Drop PHP 8.1 from CI matrix

PHP 8.1 is EOL and pest v2.36.0 now conflicts with phpunit 10.5.63,
making it impossible to run tests on PHP 8.1.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: rubenvanassche

.github/workflows/run-tests.yml

@@ -9,7 +9,7 @@ jobs:
       fail-fast: true
       matrix:
         os: [ubuntu-latest]
-        php: [8.1, 8.2, 8.3, 8.4, 8.5]
+        php: [8.2, 8.3, 8.4, 8.5]
         laravel: [10.*, 11.*, 12.*, 13.*]
         stability: [prefer-lowest, prefer-stable]
         include:
@@ -22,18 +22,12 @@ jobs:
           - laravel: 13.*
             testbench: ^11.0
         exclude:
-          - php: 8.1
-            laravel: 11.*
-          - php: 8.1
-            laravel: 12.*
           - php: 8.2
             laravel: 12.*
           - php: 8.4
             laravel: 10.*
           - php: 8.5
             laravel: 11.*
-          - php: 8.1
-            laravel: 13.*
           - php: 8.2
             laravel: 13.*
           - php: 8.5