Enable batched_api_mergeability_checks by default
What does this MR do and why?
Enable batched_api_mergeability_checks by default. It was globally enabled on production since 24th July.
MR acceptance checklist
This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.
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I have evaluated the MR acceptance checklist for this MR.
Related to #413232 (closed)