release-25.2: changefeedccl: add context cancel check to kafkav1

[rharding6373]

Backport 1/1 commits from #162058 on behalf of @rharding6373.

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Added a missing context check to handleBufferedRetries.

Epic: none
Fixes: #131223

Release note (bug fix): Fixes a bug in kafka v1 where a changefeed could potentially hang if the changefeed was shutting down.

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Release justification: Low-risk change to fix a potential hang in a deprecated feature.

[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]

It looks like your PR touches production code but doesn't add or edit any test code. Did you consider adding tests to your PR?

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

[blathers-crl]

✅ PR #162118 is compliant with backport policy

Confidence: high
Critical bug criteria met: [Stability or security issues]
Backward compatible: true
Explanation: The PR adds a missing context check to the Kafka v1 changefeed, which prevents a potential hang during changefeed shutdown. This change qualifies as fixing a critical bug related to stability issues under the 'Stability or security issues' criterion. Given that it addresses a specific bug that can affect the stability of the database, it is exempt from the feature flag requirement. The PR contains a proper release justification, describing it as a 'Low-risk change to fix a potential hang in a deprecated feature', making it clear why the backport is necessary despite it being for a deprecated feature. The file involved, 'sink_kafka.go', does not fall under any non-production category, but the nature of the fix is indeed critical as per the definitions provided.

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

[cockroach-teamcity]

This change is