flush-memcached: Replace a type: ignore with an assert.
flush-memcached: Replace a type: ignore with an assert.

Signed-off-by: Anders Kaseorg <dfdb7392591db597bc41cf266a9c3bc12a2706e5@zulip.com>

showell/zulip,kou/zulip,synicalsyntax/zulip,showell/zulip,synicalsyntax/zulip,eeshangarg/zulip,rht/zulip,eeshangarg/zulip,hackerkid/zulip,showell/zulip,eeshangarg/zulip,zulip/zulip,showell/zulip,timabbott/zulip,timabbott/zulip,synicalsyntax/zulip,eeshangarg/zulip,andersk/zulip,brainwane/zulip,kou/zulip,brainwane/zulip,kou/zulip,hackerkid/zulip,kou/zulip,andersk/zulip,kou/zulip,timabbott/zulip,andersk/zulip,rht/zulip,rht/zulip,brainwane/zulip,punchagan/zulip,hackerkid/zulip,zulip/zulip,synicalsyntax/zulip,andersk/zulip,brainwane/zulip,zulip/zulip,rht/zulip,hackerkid/zulip,rht/zulip,eeshangarg/zulip,showell/zulip,kou/zulip,kou/zulip,synicalsyntax/zulip,zulip/zulip,zulip/zulip,punchagan/zulip,showell/zulip,timabbott/zulip,brainwane/zulip,punchagan/zulip,hackerkid/zulip,andersk/zulip,timabbott/zulip,timabbott/zulip,synicalsyntax/zulip,eeshangarg/zulip,andersk/zulip,brainwane/zulip,hackerkid/zulip,zulip/zulip,eeshangarg/zulip,zulip/zulip,andersk/zulip,punchagan/zulip,synicalsyntax/zulip,rht/zulip,brainwane/zulip,punchagan/zulip,punchagan/zulip,punchagan/zulip,rht/zulip,timabbott/zulip,hackerkid/zulip,showell/zulip