In CONTRIBUTING.md "poetry shell" is used which is not part of poetry since 2.0.0.

### Bug
In CONTRIBUTING.md "poetry shell" is used instead of "poetry env activate" for poetry>=2.0.0

```
poetry shell

Looks like you're trying to use a Poetry command that is not available.

Since Poetry (2.0.0), the shell command is not installed by default. You can use,

- the new env activate command (recommended); or
- the shell plugin to install the shell command

Documentation: https://python-poetry.org/docs/managing-environments/#activating-the-environment

Note that the env activate command is not a direct replacement for shell command.
```

### Steps to reproduce
Follow CONTRIBUTING.md file.

### Python version
Python 3.11.4