[google_maps_flutter] Avoid AbstractMethod crash

[mklim]

Description

Override a default method to work around flutter/flutter#40126. The root
cause of the issue has already been fixed in master and there is a
potential workaround available to apps already, but this is an extra
low-risk change that should prevent the crash for any affected users
while the fix is still rolling out to stable.

Related Issues

flutter/flutter#40126

Checklist

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Breaking Change

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• Yes, this is a breaking change (please indicate a breaking change in CHANGELOG.md and increment major revision).
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[iskakaushik]

LGTM