Use local don't work with venvs

When I try to use pipreqs on an active venv, packages are duplicated if they exist both in the system and in the active venv.

Simple example generated requirements:
```
pandas==2.2.3 (from system)
pandas==2.2.1 (from venv) 
```

Sometimes packages are found but not written in the requirements...

Linux distro tested:
- Oracle Linux (RHEL 8.10)  
- Ubuntu (24.04.2[LTS])

CLI used:
- bash
- zsh