Fix SHOW GRANTS when partial revokes are used.

[vitlibar]

Changelog category:

• Bug Fix

Changelog entry:
Fix SHOW GRANTS when partial revokes are used. This PR fixes #31138

[Avogar]

@vitlibar Can you look at failed Functional stateless tests flaky check?

[vitlibar]

@vitlibar Can you look at failed Functional stateless tests flaky check?

It failed because the test creates some user (named test_user_01073) and the flaky check runs multiple instances of the test in multiple threads in parallel, so for the second run the user already exists and thus all those runs except the first one fail. I think we can just ignore that, it must not become a problem in master.