chore: upgrade phpunit/phpunit to ^13.1.6

Author: shimomo

.github/workflows/test.yml

@@ -21,7 +21,7 @@ jobs:
         php-version:
           - '8.4'
         phpunit-version:
-          - '12.0'
+          - '13.1.6'
     steps:
       - name: Setup PHP ${{ matrix.php-version }}
         uses: shivammathur/setup-php@accd6127cb78bee3e8082180cb391013d204ef9f

composer.json

@@ -20,7 +20,7 @@
         "nesbot/carbon": "^2.63 || ^3.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^12.0",
+        "phpunit/phpunit": "^13.1.6",
         "vimeo/psalm": "^6.0"
     },
     "autoload": {