Summary:
Original commit: d2a53ed54ad11d7a9e9acf4fcddedef6619e65e9 / D40063
`CleanupHiddenTables` is calling `Upsert` on entries without holding a COW lock which causes a segmentation fault or bad data read.
Changing the order so that we always hold the write lock.

Fixes #24929
Jira: DB-14070

Test Plan: Jenkins

Reviewers: slingam, zdrudi

Reviewed By: zdrudi

Subscribers: ybase

Differential Revision: https://phorge.dev.yugabyte.com/D40093