Use issuable reference prefix in basic search results

What does this MR do?

Uses issuable reference prefix in basic search results instead of the fixed string #. This is a regression from !46944 (merged).

Screenshots (strongly suggested)

before	after

Does this MR meet the acceptance criteria?

Conformity

• I have included a changelog entry, or it's not needed. (Does this MR need a changelog?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have self-reviewed this MR per code review guidelines.
• I have followed the style guides.

Related to #332561 (closed)