del_old_workflows.yml

name: Delete old workflow runs
on:
  schedule:
    - cron: '0 0 1 * *'
# Run monthly, at 00:00 on the 1st day of month.

  workflow_dispatch:
    inputs:
      days:
        description: 'Number of days.'
        required: true
        default: 30
      minimum_runs:
        description: 'The minimum runs to keep for each workflow.'
        required: true
        default: 6

jobs:
  del_runs:
    runs-on: ubuntu-latest
    steps:
      - name: Delete workflow runs
        uses: Mattraks/delete-workflow-runs@v2
        with:
          token: ${{ github.token }}
          repository: ${{ github.repository }}
          retain_days: 30
          keep_minimum_runs: 6