Attaching media is broken on Akkoma (possibly also Pleroma)

[rjp]

Uploading media is fine but then trying to attach it to a new status fails with a 400. Seems to be the media_ids[] being encoded to media_ids%5B%5D which is throwing things since I can get the same params to work fine if I force media_ids[] via curl. I'll add this to my list.

(I assume this will apply to anything which uses [] in a parameter.)