Environment not actually isolated

[gazpachoking]

It seems like when using this action, the environment that pdm is installed in is not actually isolated from the project. When running on python 3.7, and installing importlib-metadata 5.0.0 for the project, it seems like pdm is also using that version causing it to break. i.e. pdm-project/pdm#1411 is still manifesting. I created a very minimal repo to show what I mean:

Workflow using this action: https://github.com/gazpachoking/pdm-test/blob/master/.github/workflows/main.yml
pyproject.toml with importlib-metadata 5.0.0 dependency: https://github.com/gazpachoking/pdm-test/blob/master/pyproject.toml
pdm breaking during action run: https://github.com/gazpachoking/pdm-test/actions/runs/3261776535/jobs/5357430890

[gazpachoking]

Oh. I guess this is the same issue as pdm-project/pdm#849

My confusion is that the pdm readme says "Like Pip, PDM provides an installation script that will install PDM into an isolated environment." Maybe the default should be switched in this action to using virtualenvs instead of PEP582 if there isn't a solution to this problem?