Clearly differentiate the unresolved and resolved thread in the MR overview tab

Problem to solve

Slack thread @rdickenson brought up a great point that it is currently not clear at a glance which threads are unresolved and which are not.

Also, the below threads are both resolved but the second one (from the Changes tab) is hard to find if it is resolved or not.

Example MR - !61185 (merged)

Proposal

• Having the ✅ mark in the header for consistency.