Only update the nav bar from the top SwiftUI hosting controller.

[pixlwave]

Fixes #6833. The glitch was caused by my fix for #6738 not taking into account the embedded SwiftUI UserSuggestions module in RoomViewController, so it was modifying the navigation bar when it shouldn't have.

I've tested this change on iOS 15/16 with the auth flow and the navigation bar shows/hides as intended.

[github-actions]

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[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (hotfix/1.9.8@7f48870). Click here to learn what that means.
Patch has no changes to coverable lines.

Additional details and impacted files

@@               Coverage Diff               @@
##             hotfix/1.9.8    #6834   +/-   ##
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  Coverage                ?   53.99%           
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  Files                   ?      402           
  Lines                   ?    15772           
  Branches                ?     6342           
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  Hits                    ?     8516           
  Misses                  ?     7068           
  Partials                ?      188           

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[sonarcloud]

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