chore: update flutter to the latest version

[vaind]

This is required because we have an implicit dependency on a new core packate:web

Target of URI doesn't exist: 'package:web/web.dart'. Try creating the file referenced by the URI, or try using a URI for a file that does exist. - uri_does_not_exist

[kahest]

@getsentry/dev-infra this currently blocks our https://github.com/getsentry/sentry-dart releases, so we'd greatly appreciate your help getting this merged 🙏

[asottile-sentry]

please make sure this is a minor release when releasing this. the last couple have incorrectly made patch releases for upgrading this dependency

[kahest]

Thanks for the reminder @asottile-sentry, will do 👍

[vaind]

@kahest (or anyone else) can you please hit the merge button? I don't have the edit access.