add a cache key to venv restore plugin for easy busting

[4141done]

Proposed changes

Per the docs at for the restore-virtualenv plugin here we can specify an arbitrary cache key that adds to the key that is partially defined by the Pipfile.lock hash.

We can use this to easily bust cache when we run into python dependency issues which seems to happen every few weeks.

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have written my commit messages in the Conventional Commits format.
• I have read the CONTRIBUTING doc
• I have added tests (when possible) that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto master
• I will ensure my PR is targeting the master branch and pulling from my branch from my own fork