[google_maps_flutter] Fix incorrect comment: Change "marker" to "polyline"

[dhiaCodes]

This pull request fixes an incorrect comment in the polyline.dart file.

Fixes #155379

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene 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 linked to 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, or this PR is exempt from CHANGELOG changes.
• 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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[stuartmorgan]

Thanks for the contribution!

• 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, or this PR is exempt from CHANGELOG changes.

Which of the linked exemption reasons are you requesting an exemption under?

[dhiaCodes]

Thanks for the contribution!

• 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, or this PR is exempt from CHANGELOG changes.

Which of the linked exemption reasons are you requesting an exemption under?

Thanks for your feedback! I believe this PR is a small tweak, so I thought it might be exempt from versioning. If that's incorrect, I'd be happy to uncheck the box and make the necessary changes—I'm still learning the process.

[stuartmorgan]

I believe this PR is a small tweak, so I thought it might be exempt from versioning.

The reasons a PR would be exempt are those listed in the linked document.

[dhiaCodes]

I believe this PR is a small tweak, so I thought it might be exempt from versioning.

The reasons a PR would be exempt are those listed in the linked document.

I updated the version inside pubspec.yaml to 2.9.3
Would that work?