Describe the bug

When --force is NOT specified, the pipx inject command will still install the dependency when it exists.

How to reproduce

pipx install pycowsay
pipx inject pycowsay cowsay # inject cowsay into pycowsay for the first time
pipx inject pycowsay cowsay # inject again without `--force`, but it is still installed again

Expected behavior

Only install the injected package again when --force is specified.

BTW, I can try to submit a pull request.