Update zulip to use Color{,Swatch} asserts that tolerate float errors

[chrisbobbe]

Fixes flutter/flutter#155113.

This pulls in:
zulip/zulip-flutter@cdbe14122
zulip/zulip-flutter#949

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]

Thanks! LGTM assuming tests pass.

@gaaclarke FYI

[gaaclarke]

A lot of people are off at a conference, but I'll try to get it relanded tomorrow. Thanks.

[gnprice]

Cool, sounds good.

If you hit "approve" on this PR, then we can land this flutter/tests update to prepare for that.

(I guess the GitHub UI is offering to let me merge it already. But I think the intended policy is that PRs here require two flutter-hackers approvals to merge, just like in the main Flutter repos, and we just haven't set things up to enforce that here.)

[gnprice]

Let's see if the autosubmit bot is active here… yep!