fix: studio access notifications

[Kelketek]

Description

This pull request fixes email notifications for studio access grants. They have possibly never worked, as the tests written for them were written in such a way that bugs in the way the templates were called were not detected.

Supporting information

Internal ticket: https://tasks.opencraft.com/browse/BB-10700

Testing instructions

1. Create an account on the sandbox
2. Register a user
3. Go to the studio
4. Apply for course creator access
5. Switch to the superuser
6. Go to the Admin
7. Go to Course Creators
8. Set the status to 'granted' (you may need to check the 'all organizations' checkbox
9. Get email

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