[Development] Raising the minimum to C++20

[Sune Vuorela]

On 2023-05-03, Thiago Macieira <thiago.macieira at intel.com> wrote:
> 13, while Ubuntu 22.04 and Debian 11 (current stable) have GCC 11. Debian will 
> probably release its next stable before Qt 6.7, though whether it'll still 
> upgrade from GCC 12 to 13 I don't know. When we released Qt 6.0, our minimum 

Debian 12 "Bookworm" is planned for june 10th, and will be with gcc 12.

/Sune