mypy: Clarify return type of _check_messages_before_archiving.
mypy: Clarify return type of _check_messages_before_archiving.

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