[CI] GCC update to latest release

[rfaasse]

To be able to use the latest language features and profit from the advancements in compilers, it's proposed to update the GCC compiler in our pipelines to the latest release, currently 15.2.

[roigcarlo]

Closed via #13549. @rfaasse You can now freely use C++20 anywhere

[rfaasse]

Thank you for all the effort on this topic @roigcarlo, @loumalouomega, @RiccardoRossi and others involved! This is a big step forward (and I can imagine a significant effort) and we're very happy to have C++ 20 available in the entire code base!

This specific issue is still not completely solved, however. The GCC and Clang versions in our pipelines (the ubuntu builds) do not seem to be updated yet, meaning we cannot use all C++ 20 functionality. For an example, the ubuntu pipelines fail for this PR #13750 due to the use of std::format.

std::format is not supported for our current compilers (GCC 12 and Clang 14). Support starts at GCC 13 and Clang 17, so this functionality can be used only after the upgrades.

For reference, see https://en.cppreference.com/w/cpp/20.html for a more generic list of C++ 20 functionality support (because std::format is not the only example)

I'd propose to re-open this (and related) issue(s) until an agreement about new compilers and the upgrades themselves are reached 👍

[roigcarlo]

Ups, you'r right. Reopening. Anyway, it should be trivial to update, I will take a look next week