digests: Ensure that the teaser_data can be JSON-serialized.
digests: Ensure that the teaser_data can be JSON-serialized.

Leaving this as a set means that it fails in zerver.lib.send_email
when serializing into a ScheduledEmail object.

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