GH Actions: allow for testing on PHP 5.3

In anticipation of PR 51 being merged, I'm already adding an extra step to the `test` job.

PHP_CodeSniffer has a minimum PHP requirement of PHP 5.4, which would block the `composer install` on PHP 5.3.

By removing that `dev` dependency ahead of the `composer install`, the test workflow can also run on PHP 5.3.

Author: jrfnl

Diff for: .github/workflows/test.yml

@@ -105,6 +105,11 @@ jobs:
           php-version: ${{ matrix.php }}
           coverage: none
 
+      # Remove PHPCS as it has a minimum PHP requirements of PHP 5.4 and would block install on PHP 5.3.
+      - name: 'Composer: remove PHPCS'
+        if: ${{ matrix.php < 5.4 }}
+        run: composer remove --dev squizlabs/php_codesniffer --no-update
+
       - name: Install Composer dependencies
         uses: ramsey/composer-install@v1