release-25.2: sql: add comment about skipped FKs

[yuzefovich]

Backport 1/1 commits from #155721 on behalf of @yuzefovich.

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We just made a change to include skipped FKs (those that we deemed "irrelevant") in the commented out form. This commit improves that logic by adding a comment for why these FKs are commented out, to reduce possible confusion.

Epic: None
Release note: None

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Release justification: low-risk supportability improvement.

[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 #155730 does not comply with backport policy

Confidence: high
Explanation: The pull request appears to introduce a supportability improvement by adding comments to explain skipped foreign keys in the code. Although the PR includes a 'Release justification:' in the body indicating that it is a 'low-risk supportability improvement', this does not meet the CockroachDB backport policy for critical bugs or feature flags. The change is not behind a feature flag nor does it fix a critical bug as defined in the policy.
Recommendation: Reconsider the backport or add a feature flag to gate the change

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

[cockroach-teamcity]

This change is 

[michae2]

I disagree with blathers. This is extremely low risk and was specifically asked for by Support after an escalation.