GH Actions: show deprecations when linting

While rare, there are some deprecations which PHP can show when a file is being linted.
By default these are ignored by PHP-Parallel-Lint.

Apparently though, there is an option to show them (wasn't documented until recently), so let's turn that option on.

composer.json

@@ -62,7 +62,7 @@
       "PHPCSStandards\\Composer\\Plugin\\Installers\\PHPCodeSniffer\\Plugin::run"
     ],
     "lint": [
-      "@php ./vendor/php-parallel-lint/php-parallel-lint/parallel-lint . -e php --exclude vendor --exclude .git"
+      "@php ./vendor/php-parallel-lint/php-parallel-lint/parallel-lint . -e php --show-deprecated --exclude vendor --exclude .git"
     ],
     "test": [
       "@php ./vendor/phpunit/phpunit/phpunit --no-coverage"