Some CI maintenance

[williamfgc]

Is your feature request related to a problem? Please describe. No, just regular CI maintenance minor tasks

Describe the solution you'd like

• [x] Bump GitHub Actions version, checkout to v3
• [x] Add more debugging information $CXX -v (CXX=mpicxx, g++, clang++) and which nvcc
• [x] Remove "Start testing in-house" hint
• [x] Other tasks not associated with the above

Describe alternatives you've considered None

Additional context