[ticket/12315] Fix invalid HTML in NO_SEARCH_INDEX in language/en/acp/common.php

PHPBB3-12315
Merge remote-tracking branch 'vsephpbb/ticket/12315' into develop-ascraeus

* vsephpbb/ticket/12315:
  [ticket/12315] Fix invalid HTML in NO_SEARCH_INDEX in language/en/acp/common.php