[BUG] prevent students being in multiple classes

[hasan-sh]

Fixes #4811

How to test

• by username: invite a new student to the class.
• by link: copy the class invite link. Then switch to a student account and paste it in the browser.
• in both cases, an error should inform you that this student cannot join this class currently

[ghost]

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[Felienne]

Hi @hasan-sh!

I can't test this locally since it has the broken css files, and because of the conflicts I can't update. Can you fix the updates so I can test?

[Felienne]

Hi @hasan-sh!

I guess the easiest quick fix here (what I usually do in this type of situations where all po files have the same due to a new key) is to accept all changes from main with --theirs and then run pybabel extract again.

[Felienne]

Ah and it seems that you used the no header option on this pr originally too:

So if you run the codes again do include the header.

let me know if you need further help!

[Felienne]

Hi @hasan-sh!

Trying with an invite indeed gives the right error, but joining though a link shows:

[Felienne]

Hi @hasan-sh!

The po issues have been solved in main, so this can go in!

[mergify]

Thank you for contributing! Your pull request is now going on the merge train (choo choo! Do not click update from main anymore, and be sure to allow changes to be pushed to your fork).