fix(python): install python when pip is disabled outside virtualenv

[GabDug]

Hey 👋

As many users, I disabled pip when outside of virtual environments, to avoid messing with my global installs, using this ~/.pip/pip.conf

[global]
require-virtualenv = true

Unfortunately, it means I must always install Python with PIP_REQUIRE_VIRTUALENV=false mise install, as pip is invoked when setting up Python with mise.

This small PR adds the environment variable in the mise command invocations.

Before

➜ mise install python@3.12.0
Downloading Python-3.12.0.tar.xz...
-> https://www.python.org/ftp/python/3.12.0/Python-3.12.0.tar.xz
Installing Python-3.12.0...
Installed Python-3.12.0 to /Users/gabdug/.local/share/mise/installs/python/3.12.0
ERROR: Could not find an activated virtualenv (required).
mise ~/.local/share/mise/installs/python/3.12.0/bin/python failed
ERROR: Could not find an activated virtualenv (required).
mise ~/.local/share/mise/installs/python/3.12.0/bin/python exited with non-zero status: exit code 3
mise Run with --verbose or MISE_VERBOSE=1 for more information

After

➜ mise install python@3.12.0
Downloading Python-3.12.0.tar.xz...
-> https://www.python.org/ftp/python/3.12.0/Python-3.12.0.tar.xz
Installing Python-3.12.0...
Installed Python-3.12.0 to /Users/gabdug/.local/share/mise/installs/python/3.12.0
[notice] A new release of pip is available: 23.2.1 -> 24.0
[notice] To update, run: /Users/gabdug/.local/share/mise/installs/python/3.12.0/bin/python -m pip install --upgrade pip
mise python@3.12.0 ✓ installed 

I can try and modify the E2E test cases if you feel this would warrant a regression check.

Thanks, and have a great day!