[LyX/ next] Prepare the removal of Python 2 support

[Pavel Sanda]

On Fri, May 31, 2024 at 03:31:39PM +0200, Jean-Marc Lasgouttes wrote:
> PS: if I can get constexpr to work, I will probably ask for C++14 so that we
> can change things like
> 	static docstring foo = from_ascii("foo");

That means gcc >= 5 (or >=6.1 if we want to presume it's default). 
Given the rest of the thread (gcc>=8) bump to gcc 5/6 seems no brainer.

gcc 8 would give us C++17 (default since gcc 11).

Pavel