mypy: Amend test-backend:internet_guard to return NoReturn.
mypy: Amend test-backend:internet_guard to return NoReturn.

It is guaranteed to raise an exception, so this is reasonable,
and it satisfies mypy.

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