GCC version update in CI

[mitjarislakki]

liblsqecc/.github/workflows/build_and_test.yml

Lines 18 to 20 in d1c4e69

	env:
	CC: gcc-11
	CXX: g++-11

GCC 11 is officially no longer supported.. It also does not implement all C++20 features.
https://gcc.gnu.org/projects/cxx-status.html#cxx20

We should update to a more modern, supported compiler. I think GCC 16 (supposedly releasing this month) is a good candidate as it promises ABI stability

Some C++20 features are available since GCC 8, but support was experimental and the ABI of C++20 features was not stable until GCC 16