[webview_flutter_wkwebview] Remove unnecessary cast

[jiahaog]

This is causing an internal build to fail as it has the unnecessary_cast lint enabled.

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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[cyanglaz]

I believe this is a generated file by pigeon. Im not sure if we should edit it directly. (Probably shouldn't by looking at the comment at the beginning of the file)

cc @stuartmorgan

[stuartmorgan]

Yes, any manual edits to this file will be destroyed the next time anyone touches the plugin.

The way to fix this would be a Pigeon PR to either

• Remove the unnecessary cast in the generated code, or
• Add that lint to the suppressions at the top of the file

then do a PR for webview_flutter to update Pigeon.

[jiahaog]

Thanks! I'll close this first until we have time to follow up