[ci.yaml] Migrate bringup targets to cocoon scheduler

[CaseyHillers]

#92300

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 [Flutter Style Guide], including [Features we expect every widget to implement].
• I signed the [CLA].
• I listed at least one issue that this PR fixes in the description above.
• 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.

[keyonghan]

Are we relying on the checkout retry to bypass the issue or any other actions we have taken? What is the long term plan here?

[CaseyHillers]

Are we relying on the checkout retry to bypass the issue or any other actions we have taken? What is the long term plan here?

Yes, it should only add a minute to the recipe runs. The copybara team is working on a way to send notifications via pubsub of when mirrors complete (ETA a quarter)

[keyonghan]

LGTM

[fluttergithubbot]

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[fluttergithubbot]

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