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.

Author: jrfnl

composer.json

@@ -44,7 +44,7 @@
     "prefer-stable": true,
     "scripts" : {
         "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"
         ],
         "check-cs": [
             "@php ./vendor/squizlabs/php_codesniffer/bin/phpcs"