Allow combination of --no-venv and --no-install to suppress error on session.install

[Kxnr]

How would this feature be useful?

For normal operation, we configure nox sessions to install their (potentially heavy) requirements to simplify dependency management. In CI, we build a container including all dependencies and run the same nox sessions within the container to verify that the container built correctly. In this case, the global (container) interpreter is pre-configured with all requirements, so using --no-venv is meaningfully faster.

For sessions that call session.install, nox rightfully throws an error that the global interpreter would be modified. Adding --no-install doesn't resolve the error, however, which would be a convenient way of retaining the ability to both have sessions manage their own setup and skip setup when it's not needed.

Describe the solution you'd like

Suppress error on session.install when both --no-venv and --no-install are provided, since session.install will be a no-op with this combination of arguments.

Describe alternatives you've considered

#167 and #710 could provide other ways to create this same behavior.

Currently, we use an environment variable to skip installation when in CI and prevent an error on --no-venv. This works, but isn't ideal.

Anything else?

Potentially related to #693. I'm happy to dig in and pull together a PR if this feature is desired!

[Kxnr]

Thanks for getting this through!