[CI] Adds task to build and test plugins with macos implementations

[franciscojma86]

Description

Adds support for macOS

Related Issues

Fixes flutter/flutter#46133

Checklist

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• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See [Contributor Guide]).
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• [ x The title of the PR starts with the name of the plugin surrounded by square brackets, e.g. [shared_preferences]
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• I updated CHANGELOG.md to add a description of the change.
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Breaking Change

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[collinjackson]

LGTM though I'm not sure we need the sharding.

[collinjackson]

I wonder if we need shards. The tests should be a lot faster on macos since there's no iOS simulator to run...