test_decorators: Don't try to mutate is_staff.
test_decorators: Don't try to mutate is_staff.

Apparently, after upgrading to Django 3.2, mutating is_staff and then
saving can result in a user's session being destroyed.

In any case, this test is probably better written using two different
users with the different roles, which we have in our initial database
anyway.

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