Description:
Have an option to suppress warnings during Python installation.

Justification:
I'm using self-hosted runners in EC2 and I have constantly the WARNING: Running pip as the 'root' user can result in broken permissions and conflicting behaviour with the system package manager. It is recommended to use a virtual environment instead: https://pip.pypa.io/warnings/venv warning (which is capture by GitHub actions as an error). It would be nice to have an option to suppress these warnings so that these errors are not mixed up with the other warnings raised in the other steps.

Note: It's also not possible for me to use a non-root user when running the workflow in the EC2 instance, as explained here: machulav/ec2-github-runner#64 (comment).