autocompletion's odd behaviour with packages installed through pip

[Silejonu <silejonu@xxxxxxxx>]

Autocompletion does not work for packages installed through pip until a) the user logs out and logs back in , or b) the user deactivates the current Python venv and reactivates it. Note that, for comparison, Bash is not affected by this issue.

Steps to reproduce:

1. `python -m venv /tmp/test`
   
2. `source /tmp/test/bin/activate`
   
3. `pip install ansible`
   
4. Type `ans` and hit tab to autocomplete
   
5. Nothing happens (though syntax highlighting recognizes than `ansible` is a valid command)
   
6. `deactivate`
   
7. `source /tmp/test/bin/activate`
   
8. Type `ans` and hit tab to autocomplete
   
9. This now works correctly
   

Tested on Zsh 5.8 (CentOS Stream 9, RHEL 9) & 5.9 (Arch Linux).