`which` utility not working correctly when using `$.prefix`

[ivancuric]

The which utility doesn't use the correct path.

await $`python3 -m venv ${venvPath}`.quiet();

within(async () => { // not sure why this is needed, but doesn't work in top scope
	// activate virtual env
	$.prefix += `source ${path.join(venvPath, "bin/activate")};`;
	echo(which.sync("pip3", { nothrow: true }));	// /opt/homebrew/bin/pip3	- wrong path
	echo(await $`which pip3`.quiet()); 				// /path/to/.venv/bin/pip3	- correct path
}))

Is there a way to update the path environment variable in the script?