[ticket/12467] Add config*.php and tests_config*.php to .gitignore

PHPBB3-12467
Merge pull request #2371 from nickvergessen/ticket/12467

[ticket/12467] Add config*.php and tests_config*.php to .gitignore

* nickvergessen/ticket/12467:
  [ticket/12467] Add config*.php and tests_config*.php to .gitignore