mypy: Return AdminZulipHandler in test_logging_handlers.py.
mypy: Return AdminZulipHandler in test_logging_handlers.py.

Switching from __class__.__name__ to isinstance() allows mypy to
confirm the list comprehension type, and so the return type.

andersk/zulip,showell/zulip,shubhamdhama/zulip,timabbott/zulip,zulip/zulip,kou/zulip,punchagan/zulip,synicalsyntax/zulip,shubhamdhama/zulip,zulip/zulip,zulip/zulip,punchagan/zulip,timabbott/zulip,synicalsyntax/zulip,timabbott/zulip,tommyip/zulip,rishig/zulip,showell/zulip,timabbott/zulip,rht/zulip,zulip/zulip,synicalsyntax/zulip,shubhamdhama/zulip,andersk/zulip,rishig/zulip,showell/zulip,rishig/zulip,mahim97/zulip,rishig/zulip,dhcrzf/zulip,showell/zulip,brainwane/zulip,kou/zulip,showell/zulip,dhcrzf/zulip,dhcrzf/zulip,kou/zulip,eeshangarg/zulip,eeshangarg/zulip,dhcrzf/zulip,shubhamdhama/zulip,punchagan/zulip,punchagan/zulip,andersk/zulip,rht/zulip,mahim97/zulip,showell/zulip,andersk/zulip,shubhamdhama/zulip,brainwane/zulip,eeshangarg/zulip,tommyip/zulip,eeshangarg/zulip,brainwane/zulip,hackerkid/zulip,rht/zulip,shubhamdhama/zulip,jackrzhang/zulip,rht/zulip,jackrzhang/zulip,shubhamdhama/zulip,brainwane/zulip,tommyip/zulip,eeshangarg/zulip,synicalsyntax/zulip,andersk/zulip,jackrzhang/zulip,dhcrzf/zulip,rishig/zulip,zulip/zulip,hackerkid/zulip,kou/zulip,tommyip/zulip,mahim97/zulip,synicalsyntax/zulip,rht/zulip,zulip/zulip,tommyip/zulip,andersk/zulip,timabbott/zulip,hackerkid/zulip,rht/zulip,punchagan/zulip,eeshangarg/zulip,jackrzhang/zulip,andersk/zulip,mahim97/zulip,hackerkid/zulip,kou/zulip,punchagan/zulip,kou/zulip,jackrzhang/zulip,tommyip/zulip,rishig/zulip,brainwane/zulip,timabbott/zulip,hackerkid/zulip,synicalsyntax/zulip,rht/zulip,mahim97/zulip,brainwane/zulip,jackrzhang/zulip,hackerkid/zulip,jackrzhang/zulip,eeshangarg/zulip,timabbott/zulip,brainwane/zulip,punchagan/zulip,tommyip/zulip,kou/zulip,hackerkid/zulip,showell/zulip,zulip/zulip,dhcrzf/zulip,dhcrzf/zulip,rishig/zulip,synicalsyntax/zulip,mahim97/zulip