Incorrect email sent when added to group if user has pending invitations

[kapil1garg]

Summary
If a user is unregistered and has an existing pending invitation, inviting them to a new group causes them to receive an email with the old group that they were invited to rather than the new one.

What happened?
Tried to create and invite Darren to a CollabLab Pair Research group, but he received an email for the Segal group. In the database, Darren had not registered his account yet and had pending invitations for Segal and (now) CollabLab.

Resolution
Either send an email for the newest group, or send a template with multiple groups. Something like, "You have multiple pending invitations on Pair Research" as the subject and "You've been invited to Segal, CollabLab, etc... groups on Pair Research. Click below to log in and view your invitations"

Test cases

• User is unregistered, but has a pending invitation. When they get invited again, what email do they get?
• User is registered, but has a pending invitation. When they get invited again, what email do they get?
• Repeat with multiple pending invitations