test_auth_backends: Remove mock.patch('logging.warning').
test_auth_backends: Remove mock.patch('logging.warning').

Removed mock.patch('logging.warning') as no logs were being generated
in these blocks.

eeshangarg/zulip,kou/zulip,eeshangarg/zulip,kou/zulip,andersk/zulip,kou/zulip,hackerkid/zulip,brainwane/zulip,punchagan/zulip,hackerkid/zulip,showell/zulip,andersk/zulip,andersk/zulip,rht/zulip,zulip/zulip,punchagan/zulip,punchagan/zulip,zulip/zulip,showell/zulip,rht/zulip,rht/zulip,showell/zulip,rht/zulip,eeshangarg/zulip,kou/zulip,hackerkid/zulip,hackerkid/zulip,andersk/zulip,eeshangarg/zulip,brainwane/zulip,punchagan/zulip,brainwane/zulip,andersk/zulip,rht/zulip,andersk/zulip,brainwane/zulip,andersk/zulip,kou/zulip,kou/zulip,kou/zulip,hackerkid/zulip,hackerkid/zulip,rht/zulip,showell/zulip,zulip/zulip,brainwane/zulip,eeshangarg/zulip,punchagan/zulip,brainwane/zulip,hackerkid/zulip,showell/zulip,eeshangarg/zulip,zulip/zulip,showell/zulip,rht/zulip,zulip/zulip,brainwane/zulip,punchagan/zulip,eeshangarg/zulip,zulip/zulip,zulip/zulip,punchagan/zulip,showell/zulip