[pve-devel] [PATCH pve_flutter_frontend] navigation: replace deprecated `onPopInvoked` callback

[Shan Shaji]

Hey, thank you for the review. Removal of the library declaration was 
intentional as it's a linting issue and not necessary anymore in 
the newer versions of flutter. Added it in the same patch as 
it was a small change. 

Removal of `async` keyword was not intentional and will revert 
the change. I will document and create another patch.