Sydent produces a strange validation URL via email when sending next_link to /requestToken

[anoadragon453]

When sending the following request:

POST /_matrix/identity/api/v1/validate/email/requestToken

{
  "client_secret": "bla",
  "email": "[email protected]",
  "send_attempt": 4,
  "next_link": "whatever.com"
}

I end up with:

localhost:8090/_matrix/identity/api/v1/validate/email/submitToken?token=iYstSvVkJsWJzCyflAv1DERuvvZRZgfq&client_secret=bla&sid=1648700459&nextLink=blaaaxa.com%3Fsid%3D1648700459

in my email. Note the duplicated sid entry.

This is also on the dinsic branch. This doesn't seem to actually affect anything, as the redirect still works, but it's silly.