Pull the latest package:yaml into the SDK

[natebosch]

When I try to pull dart-archive/yaml#57 internally I get test failures in the analyzer. I have not investigated whether these failures are an indication of a real problem or a fragile test. Hopefully it's a fragile test since we'll have more difficulty if the analyzer is relying on a particular non-file defined ordering for yaml keys...

cc @yjbanov @kevmoo

[natebosch]

https://dart-review.googlesource.com/c/sdk/+/122029 gets the tests passing, but I don't know if it is safe.

cc @scheglov @bwilkerson @stereotype441

[yjbanov]

I saw these test failures in a global presubmit when trying the package:yaml change internally (and noted them in an offline email thread). They looked like brittle tests to me.