[go_router] Fix ShellRoute documentation

[mono0926]

Fixed the missing code examples in ShellRoute class - go_router library - Dart API.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter. (Unlike the flutter/flutter repo, the flutter/packages repo does use dart format.)
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I listed at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or this PR is exempt from version changes.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• All existing and new tests are passing.

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[mono0926]

Alternatively, the following may be okay.

/// final GlobalKey<NavigatorState> _rootNavigatorKey = GlobalKey<NavigatorState>();

[chunhtai]

LGTM, thanks for catching it

[auto-submit]

auto label is removed for flutter/packages, pr: 2621, due to - The status or check suite publishable has failed. Please fix the issues identified (or deflake) before re-applying this label.

[chunhtai]

can you add an entry in ChangeLog.md with ## NEXT?

[mono0926]

@chunhtai

Thanks, for the review 👍

can you add an entry in ChangeLog.md with ## NEXT?

I've added it: e08c501

[chunhtai]

@mono0926 Ah the ci suggests publishing a new version, can you publish a new version instead of using the ## NEXT?

[mono0926]

@chunhtai

can you publish a new version instead of using the ## NEXT?

done 👌