Fix --system-site-packages for upgrade --install

[ghost]

Fix #1344

• I have added a news fragment under changelog.d/ (if the patch affects the end users)

Summary of changes

The --system-site-package option currently doesn't do anything when used with upgrade --install.
This PR adds venv_args to the upgrade command so that it can be passed through to the install command, when the --install option is set.

Test plan

Tested by running

pipx upgrade --install --system-site-packages pycowsay
grep system $HOME/.local/share/pipx/venvs/pycowsay/pyvenv.cfg

Before the PR this returns:

include-system-site-packages = false

After applying the PR it returns:

include-system-site-packages = true
command = /usr/bin/python3.12 -m venv --without-pip --system-site-packages /home/sadamczyk/.local/share/pipx/venvs/pycowsay

Also successfully tested by installing https://github.com/essembeh/gnome-extensions-cli which requires the system site packages to work for the --dbus integration. Before this ran into an error because of the missing required
system dependencies.

pipx upgrade --install --system-site-packages gnome-extensions-cli
gext --dbus update --install -y nightthemeswitcher@romainvigier.fr

[chrysle]

Thanks!