[skip ci] Add missing changelog entries
What does this MR do?
Add changelog entries for 6.7.3, 6.7.4, 7.3.4.
What are the relevant issue numbers?
Does this MR meet the acceptance criteria?
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Changelog entry added -
Documentation created/updated for GitLab EE, if necessary -
Documentation created/updated for this project, if necessary -
Documentation reviewed by technical writer or follow-up review issue created -
Tests added for this feature/bug -
Job definition updated, if necessary -
Conforms to the code review guidelines -
Conforms to the Go guidelines -
Security reports checked/validated by reviewer