Backport: fix migration when commit_message_negative_regex is missing

What does this MR do and why?

Upgrade to 16.4: Migration 20230828153646 Exten... (#426066 - closed)

We have an inconsistency between database schemas. Some instances miss commit_message_negative_regex field. I suspect it's related to https://docs.gitlab.com/ee/update/package/#500-error-when-accessing-project--settings--repository.

The migration introduced in %16.4 cannot be executed for these instances.

This backport adds code to prevent migration failure when commit_message_negative_regex field does not exist.

Already fixed in master: !132908 (merged).

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
• The MR that fixed the bug on the default branch has been deployed to GitLab.com (not applicable for documentation or spec changes).
• This MR has a severity label assigned (if applicable).
• This MR has been approved by a maintainer (only one approval is required).
• Ensure the e2e:package-and-test-ee job has either succeeded or been approved by a Software Engineer in Test.

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