[go_router_builder] Add test for `onExit`#6614

auto-submit[bot] merged 10 commits intoflutter:mainflutter/packages:mainfrom

ValentinVignal:go-router-builder/Add-tests-for-on-exitValentinVignal/flutter__packages:go-router-builder/Add-tests-for-on-exitCopy head branch name to clipboard