Test encryption.create_or_replace fails intermittently with a warning

The test encryption.create_or_replace would occasionally fail with a warning message:

encryption.create_or_replace 'ctr,innodb' w2 [ fail ]  Found warnings/errors in server log file!

        Test ended at 2020-09-21 12:14:12

line

2020-09-21 12:14:06 9 [Warning] InnoDB: Trying to delete tablespace 'test/table0_int_autoinc' but there are 1 pending operations on it.

This test is effectively disabled on our CI systems, because it is marked as big test, but the failure was rather easy to repeat on 10.3 and 10.4.

This seems to have become more prominent after MDEV-23651 was fixed. The problem appears to be that fil_crypt_find_space_to_rotate() is not releasing the tablespace handle while waiting for I/O capacity, and fil_space_crypt_close_tablespace() is not waking up the threads that are in the waiting loop.