Roll cocoon tests to 5bc3916e16d57d5233a26a3d6dfcce317538f3b5

[harryterkelsen]

Rolls the cocoon checkout to 5bc3916e16d57d5233a26a3d6dfcce317538f3b5 so it picks up the fix here: flutter/cocoon#4040

This allows flutter/flutter#157755 to land without breaking customer tests.

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 the Flutter Style Guide recently, and have followed its advice.
• 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.

If you need help, consider asking for advice on the #hackers-new channel on Discord.