Using protobuf instead of ciyaml directly.

[ricardoamador]

Description

Update to flaky issues handler code so that we use the protobuf and wrappers instead of using the ciYaml directly. This will avoid issues with deprecated features as we will only receive changes via the protobuf definitions.

Issue(s)

https://github.com/flutter/flutter/issues/87529

Pre-launch Checklist

• [x] I read the Contributor Guide and followed the process outlined there for submitting PRs.
• [x] I read the Tree Hygiene wiki page, which explains my responsibilities.
• [x] I read the Flutter Style Guide recently, and have followed its advice.
• [x] I signed the CLA.
• [x] 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.

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