Remove `code_owner` ignore rule

What does this MR do?

Now that #230843 (closed) has been merged/shipped in %13.4 and we're on to %13.5, we can remove the ignore_column directive per https://docs.gitlab.com/ee/development/what_requires_downtime.html#step-3-removing-the-ignore-rule-release-m2

Related to #230836 (closed)

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Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
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• Style guides
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Availability and Testing

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• Tested in all supported browsers
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