Add a PR comment after the test run

[ryepup]

If running in a PR, it would be nice to add a comment after the test run. This would be a little more visible than the check report.

Maybe the badge and a list of any failed tests?

[AlexHedley]

Could use the outputs from action.yml.

See Comment on an issue

on:
  issues:
    types: [opened]

jobs:
  comment:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/github-script@v6
        with:
          script: |
            github.rest.issues.createComment({
              issue_number: context.issue.number,
              owner: context.repo.owner,
              repo: context.repo.repo,
              body: '👋 Thanks for reporting!'
            })