release-25.2: changefeedccl: add missing error return during change frontier startup

[andyyang890]

Backport 1/1 commits from #152364.

/cc @cockroachdb/release

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Before this change, when the change frontier encountered an error while
restoring a changefeed's span-level checkpoint, it would ignore the
error instead of moving to draining like change aggregators would.

Fixes #152104

Release note: None

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Release justification: adding missing error handling which could allow data corruption to go unnoticed

[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.}

[cockroach-teamcity]

This change is 

[blathers-crl]

✅ PR #155288 is compliant with backport policy

Confidence: high
Critical bug criteria met: [Data corruption]
Backward compatible: true
Explanation: The changes made in this PR involve modifying error handling mechanisms to address a potential data corruption issue. Specifically, it deals with an error that was previously ignored during changefeed checkpoint restoration, which would allow data corruption to go unnoticed. Such a fix is critical as it falls under the category of addressing data corruption, which is listed in the critical bug criteria. The PR contains a 'Release justification' line that specifies this change adds missing error handling to prevent unnoticed data corruption. Since this fix is related to a critical issue, it does not require feature flag gating according to the policy.

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