Lock tables before dropping the LFK trigger

What does this MR do and why?

Describe in detail what your merge request does and why.

Lock tables before dropping the LFK trigger

Removing the LFK trigger will access exclusively lock the table and that table might not be the first one to be locked for attaching it as a partition.

This changed the locking order for partitioning ci_builds by locking the builds table before the pipelines which resulted in deadlocks.

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