CI: Use conda compiler in `environment.yml`
Improvement to the conda environment to use the compiler from the virtual env instead of the system

Using the ``cxx-compile`` would be better because it will use the compiler from the virtual environment and it will not rely on the system anymore. That would be great to also avoid any kind of abi problems if someone uses some old compiler

- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry
