Upcoming GHA deprecations

[DMRobertson]

https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/ announced:

Starting 1st June 2023 workflows using save-state or set-output commands via stdout will fail with an error.

We've seen warnings about this in Synapse (e.g. here). Would it be possible to update this action to avoid this? The blog claims that

Action authors who are using the toolkit should update the @actions/core package to v1.10.0 or greater to get the updated saveState and setOutput functions.

so hopefully this should be sorted by a dependency update. (I'm not familiar with the javascript ecosystem, but I can give this a go if you'd be willing to accept the PR.)

[Kevin-M-Smith]

@DMRobertson - If you have your own fork, see the steps in either #280 or #281 to get it updated in the meantime.

[ericbn]

This GitHub Action does exactly the same as:

  - name: Cache mypy
    uses: actions/cache@v3
    with:
      path: .mypy_cache
      key: mypy-cache-${{ github.sha }}
      restore-keys: mypy-cache-

The implementation could be refactored to be as simple as that (using actions/cache instead of reimplementing it).

Personally, I've added the mypy version to the cache key, as I've experienced issues with old caches after upgrading the mypy version being used:

  - name: Get mypy version
    id: mypy-version
    run: |
      echo "mypy-version=$(mypy --version | awk '{print $2}')" >> $GITHUB_OUTPUT
  - name: Cache mypy
    uses: actions/cache@v3
    with:
      path: .mypy_cache
      key: mypy-cache-${{ steps.mypy-version.outputs.mypy-version }}-${{ github.sha }}
      restore-keys: mypy-cache-${{ steps.mypy-version.outputs.mypy-version }}-