[go_router_builder] Support analyzer 13

[simolus3]

This declares support for analyzer versions 13.x in the go_router_builder package.

I ran tool/run_tests.dart after upgrading, no code changes are necessary and existing tests pass. Note that another package in this repository, pigeon, also depends on an older analyzer version but would require code changes to support analyzer version 13.x.

Closes flutter/flutter#189357.

Pre-Review Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the AI contribution guidelines and understand my responsibilities, or I am not using AI tools.
• I read the Tree Hygiene page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter.
• 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 linked to at least one issue that this PR fixes in the description above.
• I followed the version and CHANGELOG instructions, using semantic versioning and the repository CHANGELOG style, or I have commented below to indicate which documented exception this PR falls under[^1].
• I updated/added any relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or I have commented below to indicate which test exemption this PR falls under[^1].
• All existing and new tests are passing.

Comments below:

• There is no relevant documentation to update.
• This change is covered by existing tests, so I have not added new ones.

[gemini-code-assist]

Code Review

This pull request updates the analyzer dependency constraint in packages/go_router_builder/pubspec.yaml to support version 13 (allowing <14.0.0) and updates the CHANGELOG.md accordingly. There are no review comments, and I have no feedback to provide.

[stuartmorgan-g]

Thank you for your contribution! Because of the volume of PRs we receive, we require that new contributors use our checklist to guide them through critical steps in creating a Flutter PR. This PR's description is missing that checklist, so it is being marked as a Draft.

Please edit the PR description to add the checklist, then ensure that you have completed all of the steps. Once you've done that, please mark the PR as ready for review.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

[gemini-code-assist]

Code Review

This pull request updates the go_router_builder package to version 4.3.1, extending the supported range of the analyzer dependency to <14.0.0 and updating the changelog accordingly. There are no review comments, and I have no feedback to provide.

[simolus3]

Apologies for causing extra work here, I assumed it would be fine for a tiny change but I shouldn't have skipped that. I have created an issue and filled out the checklist now.