RedirectRegex example does not work in Rancher 2.6

We use Nextcloud in our K3S Rancher setup. Therefore we need to redirect the CalDAV/CardDAV routes. The Traefik documentation says in its Configuration Example of RedirectRegex that we have to use this as labels.

  - "traefik.http.middlewares.test-redirectregex.redirectregex.regex=^/.well-known/ca(l|rd)dav"
  - "traefik.http.middlewares.test-redirectregex.redirectregex.replacement=/remote.php/dav/"

Entering this in Rancher UI results in the follow error:

The label key is too long and the regex is not allowed as key. Are there any solutions available?