release-25.3: 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 the change does not break backwards compatibility and otherwise complies with the backport policy. Include a brief release justification in the PR description explaining why the backport is appropriate. All backports must be reviewed by the TL for the owning area. While the stricter LTS policy does not yet apply, please exercise judgment and consider gating non-critical changes behind a disabled-by-default feature flag when appropriate.

[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