Elasticsearch merge request search by IID requires `#1` syntax

Summary

Elasticsearch allows you to search issues and MRs by IID, if you use the reference form (#1 for issues, !1 for MRs). Unfortunately, MRs actually check for # instead of ! before taking this path.

Steps to reproduce

Search MRs for !1 then #1

What is the current bug behavior?

The first form fails, the second works

What is the expected correct behavior?

The first form succeed, the second fail

Relevant logs and/or screenshots

(Paste any relevant logs - please use code blocks (```) to format console output, logs, and code as it's very hard to read otherwise.)