mypy: Fix a buggy annotation in create_mirrored_message_users.
mypy: Fix a buggy annotation in create_mirrored_message_users.

j831/zulip,vabs22/zulip,jackrzhang/zulip,Galexrt/zulip,Galexrt/zulip,timabbott/zulip,christi3k/zulip,brainwane/zulip,jackrzhang/zulip,showell/zulip,synicalsyntax/zulip,shubhamdhama/zulip,j831/zulip,hackerkid/zulip,andersk/zulip,dhcrzf/zulip,showell/zulip,verma-varsha/zulip,tommyip/zulip,punchagan/zulip,vaidap/zulip,brainwane/zulip,Galexrt/zulip,rht/zulip,eeshangarg/zulip,amanharitsh123/zulip,dhcrzf/zulip,jackrzhang/zulip,amanharitsh123/zulip,zulip/zulip,Galexrt/zulip,rishig/zulip,verma-varsha/zulip,punchagan/zulip,dhcrzf/zulip,synicalsyntax/zulip,eeshangarg/zulip,hackerkid/zulip,brockwhittaker/zulip,tommyip/zulip,christi3k/zulip,jrowan/zulip,rishig/zulip,jrowan/zulip,synicalsyntax/zulip,punchagan/zulip,showell/zulip,zulip/zulip,rishig/zulip,tommyip/zulip,hackerkid/zulip,verma-varsha/zulip,vaidap/zulip,vabs22/zulip,Galexrt/zulip,shubhamdhama/zulip,kou/zulip,vaidap/zulip,hackerkid/zulip,brockwhittaker/zulip,andersk/zulip,brockwhittaker/zulip,mahim97/zulip,vabs22/zulip,brainwane/zulip,shubhamdhama/zulip,jrowan/zulip,shubhamdhama/zulip,mahim97/zulip,timabbott/zulip,showell/zulip,andersk/zulip,christi3k/zulip,zulip/zulip,timabbott/zulip,jackrzhang/zulip,verma-varsha/zulip,timabbott/zulip,hackerkid/zulip,rht/zulip,verma-varsha/zulip,vabs22/zulip,mahim97/zulip,jackrzhang/zulip,shubhamdhama/zulip,hackerkid/zulip,andersk/zulip,zulip/zulip,eeshangarg/zulip,mahim97/zulip,punchagan/zulip,tommyip/zulip,jrowan/zulip,zulip/zulip,Galexrt/zulip,dhcrzf/zulip,rht/zulip,synicalsyntax/zulip,zulip/zulip,kou/zulip,synicalsyntax/zulip,andersk/zulip,showell/zulip,j831/zulip,kou/zulip,timabbott/zulip,brockwhittaker/zulip,vabs22/zulip,dhcrzf/zulip,christi3k/zulip,j831/zulip,vaidap/zulip,amanharitsh123/zulip,rht/zulip,punchagan/zulip,showell/zulip,Galexrt/zulip,rht/zulip,synicalsyntax/zulip,brainwane/zulip,rht/zulip,showell/zulip,brockwhittaker/zulip,shubhamdhama/zulip,eeshangarg/zulip,rishig/zulip,mahim97/zulip,vaidap/zulip,christi3k/zulip,tommyip/zulip,jrowan/zulip,j831/zulip,andersk/zulip,tommyip/zulip,vaidap/zulip,amanharitsh123/zulip,punchagan/zulip,dhcrzf/zulip,brockwhittaker/zulip,rishig/zulip,kou/zulip,punchagan/zulip,shubhamdhama/zulip,amanharitsh123/zulip,eeshangarg/zulip,dhcrzf/zulip,rishig/zulip,eeshangarg/zulip,brainwane/zulip,brainwane/zulip,kou/zulip,synicalsyntax/zulip,brainwane/zulip,verma-varsha/zulip,rishig/zulip,vabs22/zulip,kou/zulip,jackrzhang/zulip,mahim97/zulip,andersk/zulip,timabbott/zulip,jrowan/zulip,amanharitsh123/zulip,zulip/zulip,jackrzhang/zulip,rht/zulip,christi3k/zulip,eeshangarg/zulip,j831/zulip,kou/zulip,hackerkid/zulip,tommyip/zulip,timabbott/zulip