Missing AGENT_TOOLSDIRECTORY env variable for setup-python@v2

[mjpieters]

The setup-python@v2 action makes the following assumptions:

• On linux, the /etc/lsb-release file is read and the DISTRIB_RELEASE=... value must match the platform_version keys in the Python versions manifest. In practice this means the container must be based on Ubuntu.
• Once downloaded, each Python version has a setup.sh file, generated from a template that assumes the AGENT_TOOLSDIRECTORY env variable exists; this is just an alias for RUNNER_TOOL_CACHE.
• The python -m pip install --ignore-installed pip upgrade step requires SSL libraries to be installed (openssl)

So I can make the action work by:

• Using my own Ubuntu-based docker image (mjpieters/act-container:18.04, which is just node:buster-slim but using ubuntu:18.04 rather than Debian Buster, with openssl added; 180MB small, see https://hub.docker.com/repository/docker/mjpieters/act-container)

• adding the following build step:

  env:
      AGENT_TOOLSDIRECTORY: ${{ runner.tool_cache }}

While I understand that the node:*-slim containers are only meant to be starter images, could act be updated to provide the AGENT_TOOLSDIRECTORY variable?

Test workflow:

name: Run testsuite

on:
  push

jobs:
  test:
    name: Run Python
    runs-on: ubuntu-latest
    env:
        AGENT_TOOLSDIRECTORY: ${{ runner.tool_cache }}
    steps:
    - name: Set up Python 3.7
      uses: actions/setup-python@v2
      with:
        python-version: 3.7
    - name: Test Python
      run: |
        python -V

[mjpieters]

This appears to be a python-versions bug instead. It was already fixed in the Windows install script, so I proposed a fix for the Linux version.