release-25.2: changefeedccl: fix reversed args for containment check in test logic

[blathers-crl]

Backport 1/1 commits from #152880 on behalf of @nicktrav.

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Fix a testing bug introduced in #131545 where the Contains check arguments were reversed. The error string being searched should precede the string being searched for. The examples from the API docs:

//	require.Contains(t, "Hello World", "World")
//	require.Contains(t, ["Hello", "World"], "World")
//	require.Contains(t, {"Hello": "World"}, "Hello")

Release note: None

Epic: None

---

Release justification: Test only.

[blathers-crl]

Thanks for opening a backport.

Before merging, please confirm that it falls into one of the following categories (select one):

• Non-production code changes. Includes test-only changes, build system changes, etc.
• Fixes for serious issues. Defined in the policy as correctness, stability, or security issues, data corruption/loss, significant performance regressions, breaking working and widely used functionality, or an inability to detect and debug production issues.
• Other approved changes. These changes must be gated behind a disabled-by-default feature flag unless there is a strong justification not to.

Add a brief release justification to the PR description explaining your selection.

Also, confirm that the change does not break backward compatibility and complies with all aspects of the backport policy.

All backports must be reviewed by the TL and EM for the owning area.

[blathers-crl]

✅ PR #153210 is compliant with backport policy

Confidence: high
Backward compatible: true
Explanation: The pull request is compliant with backport policy because the changes are limited to a non-production file classified under the test file patterns (*_test.go). The PR specifically modifies a file named 'errors_test.go', which, according to the defined CockroachDB backport policy, exempts it from requiring gating behind a feature flag or critical bug fixes since it only affects test logic. Additionally, the PR body mentions 'Release justification: Test only.' which further aligns with the policy allowances for testing-related changes. As the changes pertain solely to test logic correction (specifically checking argument order in assertions), there is no implication on production code, no feature flag requirement, and the changes inherently maintain backward compatibility.

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[cockroach-teamcity]

This change is 

[nicktrav]

TFTR!