populate_db: Re-enable push_notifications logger.
populate_db: Re-enable push_notifications logger.

We were disabling push_notifications logger but weren't enabling
it back. This caused failures on porting logging mocks to assertLogs
as assertLogs expects a log to be generated.

See 9c224ccdd392ca29bcca4277f7a94393f5be3cb6 for why we disable
these. (To avoid logs spam from push_notifications_logger)

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