mgr/ActivePyModules.cc: always release GIL before attempting to acquire a lock

mgr/ActivePyModules.cc: always release GIL before attempting to acquire a lock

A thread that holds the GIL while attempting to acquire a mutex will cause a deadlock
if another thread owns the mutex and is waiting on the GIL. The GIL must not be treated
like an ordinary mutex since it may be preempted at any time or released when doing
blocking I/O. Such deadlocks are severe since they starve all threads from access to the
GIL and therefore prevent any Python code from running until the mgr process is restarted.

Fixes: https://tracker.ceph.com/issues/39264
Signed-off-by: Cory Snyder <csnyder@iland.com>