[ticket/11288] add search tests cases

PHPBB3-11288
[ticket/11288] fix regex in postgres

Postgres search backend now uses updated regex being used by
mysql search backend.

PHPBB3-11288
Merge PR #1388 branch 'dhruvgoel92/ticket/11288' into develop

# By Dhruv
# Via Dhruv
* dhruvgoel92/ticket/11288:
  [ticket/11288] fix regex in postgres
  [ticket/11288] add search tests cases