Fix existing code linting issues, make CI PHP Lint job fail if code style violations are detected (#384)

* Make CI `PHP Lint` job fail if code style violations are detected

Currently there are linting violations, but the `PHP Lint` job is still passing.

https://github.com/Kyon147/laravel-shopify/actions/workflows/lint.yml

Most recent example: https://github.com/Kyon147/laravel-shopify/actions/runs/12164298709/job/33925618006

This change should ensure that the CI job will fail if PHP CS Fixer detects linting violations.

* Fix existing linting issues

vendor/bin/php-cs-fixer fix
PHP CS Fixer 3.68.3 Persian Successor by Fabien Potencier, Dariusz Ruminski and contributors.
PHP runtime: 8.3.16
Running analysis on 1 core sequentially.
You can enable parallel runner and speed up the analysis! Please see usage docs for more information.
Loaded config default from "laravel-shopify/.php-cs-fixer.dist.php".
Using cache file ".php-cs-fixer.cache".
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   1) src/resources/routes/shopify.php
   2) src/resources/routes/api.php
   3) src/Http/Middleware/VerifyScopes.php

Fixed 3 of 216 files in 0.072 seconds, 18.00 MB memory used

Author: thejamescollins

.github/workflows/lint.yml

@@ -31,4 +31,4 @@ jobs:
           composer install --no-interaction --prefer-dist
 
       - name: Check for code style violation with PHP-CS-Fixer
-        run: vendor/bin/php-cs-fixer fix --diff
+        run: vendor/bin/php-cs-fixer check