Summary:
FlagsCallbackRegistry::InvokeCallbacks invokes callbacks while holding flag callbacks mutex.
It is antipattern, since such behaviour could lead to deadlock.
Thread sanitizer detects this possible deadlock.

This diff fixes the issue by releasing lock before invoking callbacks.
Jira: DB-13588

Original commit: 4aa590217c5f4bf9a70e61b455404aaaefb63f3b / D39291

Test Plan: ybd tsan --gtest_filter PgCatalogVersionTest.DisableNopAlterRoleOptimization

Reviewers: hsunder, timur

Reviewed By: hsunder, timur

Subscribers: ybase

Tags: #jenkins-ready

Differential Revision: https://phorge.dev.yugabyte.com/D54755