**Backport:** https://codeberg.org/forgejo/forgejo/pulls/10056
- Matrix room v12 made the room ID domain-less.
- The exact format varies across room versions, so don't try to give a
new regular expression, simply require the input starts with `!`.
- Resolvesforgejo/forgejo#9341
Co-authored-by: Gusted <postmaster@gusted.xyz>
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/10064
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Co-authored-by: forgejo-backport-action <forgejo-backport-action@noreply.codeberg.org>
Co-committed-by: forgejo-backport-action <forgejo-backport-action@noreply.codeberg.org>