`pipx upgrade --install` ignores `--system-site-packages` option

Describe the bug

Recently in this PR the --install option was added to the upgrade command.
Unfortunately this doesn't seem to respect the --system-site-packages option.

How to reproduce

When using upgrade --install the --system-site-packages option isn't respected:

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

Comparison with the install command, where it works correctly:

❯ pipx install --system-site-packages pycowsay
❯ grep system $HOME/.local/share/pipx/venvs/pycowsay/pyvenv.cfg
include-system-site-packages = true
command = /usr/bin/python3 -m venv --without-pip --system-site-packages /home/sadamczyk/.local/share/pipx/venvs/pycowsay

Expected behavior

The upgrade --install command should handle the --system-site-packages option just like the install command does.

Investigation

Looking through the code, the --system-site-packages option seems to be passed to the install command in the venv_args variable from the get_venv_args function:

pipx/src/pipx/main.py

Lines 170 to 174 in 5482fac

	def get_venv_args(parsed_args: Dict[str, str]) -> List[str]:
	venv_args: List[str] = []
	if parsed_args.get("system_site_packages"):
	venv_args += ["--system-site-packages"]
	return venv_args

pipx/src/pipx/main.py

Line 182 in 5482fac

venv_args = get_venv_args(vars(args))

But venv_args is only passed to the run, install and install-all commands

pipx/src/pipx/main.py

Lines 244 to 253 in 5482fac

	elif args.command == "install":
	return commands.install(
	None,
	None,
	args.package_spec,
	paths.ctx.bin_dir,
	paths.ctx.man_dir,
	args.python,
	pip_args,
	venv_args,

... but not to the upgrade command:

pipx/src/pipx/main.py

Lines 294 to 304 in 5482fac

	elif args.command == "upgrade":
	return commands.upgrade(
	venv_dirs,
	args.python,
	pip_args,
	verbose,
	include_injected=args.include_injected,
	force=args.force,
	install=args.install,
	python_flag_passed=python_flag_passed,
	)

It might be enough to add the required function arguments so that the venv_args from the main.py can be passed through all the way to the install call here:

pipx/src/pipx/commands/upgrade.py

Lines 111 to 114 in 5482fac

	if install:
	commands.install(
	venv_dir=None,
	venv_args=[],

[chrysle]

Although the --install option is merely meant as a backup (e. g. for automation), and still pipx install should be used to enable more customization, probably it wouldn't hurt to implement your suggestion. Would you like to do this yourself?

@chrysle Sure, I can try implementing it. I'll take a look in the coming weeks.