pypy3 does not install latest #296

Description:
I want to use the latest stable pypy release for 3.x. I didn't see a way to do this in the docs, but the action did accept pypy3, however this installs 3.6.12, which looks like the latest version of 3.6 in versions.json.

If there is another way to use the latest version of 3.x, please let me know. I think this is a bug either way, as it is intuitive and accepted, yet doesn't provide intuitive behavior.

Action version:
actions/setup-python@v2

Platform:

• Ubuntu
• macOS
• Windows

Runner type:

• Hosted
• Self-hosted

Tools version:
pypy3.x

Repro steps:
You can see in this workflow, under the pypy3 job.

matrix.python-version is set to pypy3

  - name: Set up Python ${{ matrix.python-version }}
    uses: actions/setup-python@v2
    with:
      python-version: ${{ matrix.python-version }}

Expected behavior:
The latest stable version supporting Python 3.x should be installed

Actual behavior:
pypy3.6 (3.6.12) is installed