Django 2.2 and 3.0 don't support settings samesite='None' in
HttpResponse.set_cookie() so fix is not necessary and will not be
backported.
Backport of 9bc8b1ad2d from master
Cookies with the "SameSite" flag set to None and without the "secure"
flag will be soon rejected by latest browser versions.
This affects sessions and messages cookies.
Backport of 240cbb63bf from master