Enable GitHub workflow on pull requests

[moorereason]

Can the GH workflow be enabled on pull_request instead of just push? I don't think it would trigger a release since the workflow checks for tags before doing that.

I was thinking of changing the workflow to use:

on:
  push:
  pull_request:
    paths-ignore:
      - '**.md'

[tierpod]

I checked GH workflow documentation and it should be fine. Merged as #56. Thank you for the improvement suggestion!