test_push_notifications: Fix mock_apns type.
test_push_notifications: Fix mock_apns type.

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

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