[Bug] Multiple users cannot subscribe to the same playlist

[xortuna]

Describe the bug
No more than 1 user can subscribe to the same playlist, The trash icon appears for other users on the playlist page which does not function, attempting to call subscribe_playlist manually causes a 500 error with:

duplicate key value violates unique constraint "playlists_pkey" (PQ::PQError)

Steps to Reproduce

1. Under account A locate and subscribe to a playlist by clicking the '+' button on the playlist's page
2. Log out of account A and log into Account B
3. Attempt to subscribe to the same playlist

[SamantazFox]

Thanks for reporting this issue!

[methosinhiding]

Just re-confirming that this is still an active issue as of the '2023.09.18-bb14f79 @ master' docker install.