Describe the bug
The very first time setup-python is called for a specific version on a self hosted runner, the action will download files into the GITHUB_WORKSPACE and leave them there.

This causes issues for later steps, for instance if I have a step to run linters it runs on the temporary files setup-python downloads.

Which version of the action are you using?

• v1
• v2
• Some other tag (such as v2.0.1 or master)

Environment

• self-hosted
• Linux
• Windows
• Mac

If applicable, please specify if you're using a container

Python Versions
Please list all of the effected versions of Python (3.8.2, etc.)

To Reproduce

This workflow file run on a self-hosted Ubuntu 18.04 linux server will reproduce:

name: Test setup-python workspace
on: push
jobs:
  test:
    name: Test setup-python
    runs-on: [self-hosted, linux]
    steps:
      - uses: actions/checkout@v2
      - name: before
        run: |
          ls
          ls $GITHUB_WORKSPACE
          du -hc ./
      - name: setup python
        uses: actions/setup-python@v2
        with:
          python-version: 2.7.17
      - name: after
        run: |
          ls
          ls $GITHUB_WORKSPACE
          du -hc ./

After running this you should see a directory with a UUID that adds approximately ~130MB of files to the workspace.

Run/Repo Url
If applicable, and if your repo/run is public, please include a URL so it is easier for us to investigate.

Screenshots
If applicable, add screenshots to help explain your problem.

Additional context
Add any other context about the problem here.