Don't waste time on a test that's guaranteed to fail

.gitlab-ci.yml

@@ -26,7 +26,6 @@ before_script:
 
   # PHP extensions
   - docker-php-ext-install mbstring mysqli intl gd zip bz2
-  - docker-php-ext-enable mbstring mysqli intl gd zip bz2
 
   # Install Composer
   - curl -sS https://getcomposer.org/installer | php
@@ -55,6 +54,7 @@ PHPunit:PHP5.3:MySQL:
   script:
     - phpcs -n
     - phpunit
+  when: manual
   allow_failure: true
 
 PHPunit:PHP5.6:MySQL: