Fix tests for invites

[alneberg]

Will try to add tests for invites that cover all the regular use cases. Opened a PR mostly to show/track progress.

Before submitting a pr:

• Tests passing
• Black formatting
• Migrations for any changes to the database schema
• Rebase/merge the dev branch
• Note in the CHANGELOG

[codecov]

Codecov Report

Merging #907 (9a00609) into dev (aded197) will not change coverage.
The diff coverage is n/a.

❗ Current head 9a00609 differs from pull request most recent head 3099cd1. Consider uploading reports for the commit 3099cd1 to get more accurate results

@@           Coverage Diff           @@
##              dev     #907   +/-   ##
=======================================
  Coverage   86.13%   86.13%           
=======================================
  Files          26       26           
  Lines        2812     2812           
=======================================
  Hits         2422     2422           
  Misses        390      390           

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[alneberg]

Closing since #912 has taken its place.