Clean up GitHub caches after closing PRs

[redeboer]

The Pixi caches stored for the GitHub workflows are quite large, see here. It would be better to automatically remove the caches for the PRs once they are closed. You can do so with this workflow:

name: Clean caches

on:
  pull_request:
    types:
      - closed
  workflow_dispatch:
    inputs:
      ref:
        description: Clean caches for this branch name or ref
        required: false
        type: string

jobs:
  cleanup:
    name: Remove caches
    runs-on: ubuntu-22.04
    steps:
      - uses: ComPWA/actions/clean-caches@v1
        with:
          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
          ref: ${{ inputs.ref }}