Disables zulip.test

[gaaclarke]

fixes: flutter/flutter#155113

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.

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[gnprice]

When disabling a test suite in this repo, we do it by renaming the file, not deleting it. See git log -p registry/.

In any event I don't think there's a reason to disable these tests. As the repo's README says:

Remove the test in question. This is by far the least ideal solution. To go down this path, we must first establish that one of the following is true:

• the people listed as contacts for the test are not responsive (within 72 hours).
• the test is poorly written (e.g. it contains a race condition or relies on assumptions that violate clearly documented API contracts), and the people listed as contacts are not willing to fix the test or accept fixes for the test.
• we have gone through the breaking change process cited above, but are unable to update the test accordingly (e.g. the people listed as contacts are not willing to work with us to update their code).

None of those apply here. The breaking change process is ongoing, in the threads flutter/flutter#155113 and flutter/flutter#155262 . That framework PR to enable the migration was sent a couple of hours ago and hasn't yet landed.

[gnprice]

Closing in favor of #409.