Hermit overwrites user-set PATH when installing packages

[alecthomas]

This came to light while using Python's virtual env.

(.venv) 🐚 ~/Projects/hermit $ echo $PATH
/Users/aat/Projects/hermit/.venv/bin:/Users/aat/Projects/hermit/bin:/Users/aat/Projects/hermit/.hermit/go/bin:/Users/aat/bin:/opt/homebrew/bin:/opt/homebrew/bin:/opt/homebrew/sbin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/opt/local/bin:/usr/local/munki:/Applications/kitty.app/Contents/MacOS:/opt/homebrew/opt/fzf/bin
(.venv) 🐚 ~/Projects/hermit $ hermit install jq
info:jq-1.6:install: Installing jq-1.6
(.venv) 🐚 ~/Projects/hermit $ echo $PATH
/Users/aat/Projects/hermit/bin:/Users/aat/Projects/hermit/.hermit/go/bin:/Users/aat/bin:/opt/homebrew/bin:/opt/homebrew/bin:/opt/homebrew/sbin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/opt/local/bin:/usr/local/munki:/Applications/kitty.app/Contents/MacOS:/opt/homebrew/opt/fzf/bin

Note how .venv/bin has been removed.