Cookies are set twice in the HTTP header

[RichardPautz]

The set-cookie parameter is always set twice in the HTTP header.
This happens on all grav based sites I looked at, whether I curl -I "https://getgrav.org" or one of the sites in the "Build with Grav" section, like https://trilby.media/ or https://www.oblique.space or even my own localhost.

[mahagr]

I think this might be side effect from a fix with no cookie being sent in older versions of PHP.