Dismiss the file tree popover if it block access o the branch selector

What does this MR do and why?

Fixes #361403 (closed)
This change ensures we dismiss the popover every time it appears.

The test only dismisses the popover upon initializing the page, but when you navigate some more it reappears.
To dismiss the popover permanently we would need to interact with the popover as per !85874 (diffs) 'Permanently' means it sets a value in the localStorage now, so when we run the test again in a clean browser, it will appear again so we will need to continually handle this situation until it is stored in the DB in the longer term.

Error can be easily reproduced: #361403 (comment 938977676)

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