[go_router] Fix a typo in the ShellRoute docstring

[emesterhazy]

Remove an extraneous "that" and an unnecessary comma.

This is just a simple typo fix for the docstring comment above the ShellRoute class.
Assuming I am correct that this is a typo, I think it makes the documentation a little
more difficult to read.

There is no issue open to track this, but I can create one if it's really necessary.
I'm going to check the box in the pre-launch checklist anyways 🙈

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.

[chunhtai]

LGTM

[johnpryan]

Thanks!

[auto-submit]

auto label is removed for flutter/packages, pr: 3378, due to - The status or check suite repo_checks has failed. Please fix the issues identified (or deflake) before re-applying this label.

[auto-submit]

auto label is removed for flutter/packages, pr: 3378, due to - The status or check suite repo_checks has failed. Please fix the issues identified (or deflake) before re-applying this label.

[johnpryan]

Hmm, I'm wondering why we can't submit this? This shouldn't need version change, so we added the "override: no versioning needed" label, but it's saying that "the change to this package could not be verified to be exempt from version changes according to repository policy"

[chunhtai]

forgot to rerun the check after applying the label, rerunning