test_signup: Fix typo in test name.
test_signup: Fix typo in test name.

andersk/zulip,rht/zulip,rht/zulip,zulip/zulip,zulip/zulip,rht/zulip,zulip/zulip,rht/zulip,zulip/zulip,rht/zulip,rht/zulip,andersk/zulip,andersk/zulip,andersk/zulip,zulip/zulip,andersk/zulip,zulip/zulip,rht/zulip,andersk/zulip,andersk/zulip,zulip/zulip