Makes the file test exempt. We could alternately count it as a test, but I think it is rare (and not a great practice) for someone to test the changes in their PR exclusively by modifying an element of the customer tests.

Motivated by flutter/flutter#167754

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This pulls in the 4 commits below:

flutter/tests@8be7209...c9cbc60

2025-04-24 [email protected] Bump Zulip pin to update sliver z-order tests
(flutter/tests#456) 2025-04-17
[email protected] Revert "Disable
flutter_devtools.test" (flutter/tests#455) 2025-04-15 [email protected]
Update zulip hash to pick up version that can be analyzed cleanly.
(flutter/tests#453) 2025-04-15 [email protected] Disable
flutter_devtools.test (flutter/tests#452)

(using the command from 5ce5251 / flutter#162763 to make the log).

The two changes from 2025-04-15 had been here since db68c95 (flutter#16721),
but then it looks like they were accidentally reverted earlier today by
417f47f (flutter#165596).

The change from 04-17 doesn't appear to have made it here to
flutter/flutter yet.

The latest change just went into flutter/tests today and is why I'm
making this PR.

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