more descriptive output when shell is active and venv is deactivated

[bmarroquin]

Pull Request Check List

Relates to: #5323

• [x] Added tests for changed code.

It looks like there is confusion with how poetry shell and deactivate interact with each other. This changes the output to be a little more descriptive. Also adds minor tests to the shell command

[Secrus]

Hi, @bmarroquin are you still interested in bringing this to Poetry?

[Secrus]

Closing, since it's almost a year with no response

[github-actions[bot]]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.