The customer_testing test uses a version of flutter/test determined by the initial branch point of the PR, found via https://github.com/flutter/flutter/blob/master/dev/tools/bin/find_commit.dart:

This causes problems in PRs for people who use a merge workflow to get new versions of master (which is the only one supported by the GitHub UI); the merge will make the PR up to date for the purposes of every test except for customer_testing, creating exactly the kind of mismatch that the script is intended to avoid. The only way to fix a PR in that state is to rebase (from a local checkout) and force-push, which is much less convenient. It's also a very weird failure state; the only way to know this is to have it happen to you, be confused, and ask, which is a frustrating experience for developers.

If possible, when there has been a merge from the original branch find_commit should use the last merged commit instead of the original branch commit to determine the anchor date.