Fix minor scope switching bug in command palette

What does this MR do and why?

Fix minor scope switching bug in command palette

If you e.g. search for projects with :test and switch it to search for users by only replacing the : -> @, the command-palette wouldn't search again, as it only was watching the "search-string" for changes.

Screenshots or screen recordings

Before	After
Screen_Recording_2023-07-12_at_15.07.33	Screen_Recording_2023-07-12_at_15.06.02

How to set up and validate locally

1. In rails console enable the experiment fully

   Feature.enable(:command_palette)

2. Visit any group or project member pages such as http://127.0.0.1:3000/groups/flightjs/-/group_members
3. Type @test and replace @ with :

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.