Add this Github Action to your repo to notify you when branches are stale and delete them if no action is taken. If you would like to keep your branch alive, you may prefix it with keep-alive- It pulls the slack credentials from Github, thus your slack and github account must be associated with the same email.

You can use the action from this example repository:

name: Purge Branches
on:
  schedule:
    - cron: '0 10 * * *' # every day @ 10 AM UTC
jobs:
  purgeBranches:
    runs-on: ubuntu-latest
    steps:
      - name: Delete & Notify Branches
        uses: gita-vahdatinia/purge-branchn@v1
        with:
            token: ${{ secrets.GITHUB_TOKEN }}
            days-to-notify: 50
            days-to-delete: 100