tests: Fix moderator comment in new-members stream-policy test.
tests: Fix moderator comment in new-members stream-policy test.

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