Delete .github/workflows/backup.yml (#236)

This hasn't been working in ages and also probably wasn't a useful idea to begin with.

.github/workflows/backup.yml

@@ -1,34 +0,0 @@
-name: Backup
-
-on:
-  schedule:
-    - cron: '5 4 * * 0'
-
-  workflow_dispatch:
-
-jobs:
-  backup:
-    runs-on: ubuntu-20.04
-    timeout-minutes: 60
-
-    steps:
-      - name: Configure cache
-        uses: actions/cache@v4
-        with:
-          path: |
-            ${{ env.GITHUB_WORKSPACE }}
-            ~/.cache/restic
-          key: ${{ runner.os }}
-
-      - name: Install the correct Python version
-        uses: actions/setup-python@v5
-        with:
-          python-version: '3.x'
-
-      - name: Run backup action
-        uses: julia-actions/restic-action@main
-        env: # Options: https://restic.readthedocs.io/en/latest/040_backup.html#environment-variables
-          RESTIC_REPOSITORY: b2:${{ secrets.B2_BUCKET }}:${{ github.repository }}
-          RESTIC_PASSWORD: ${{ secrets.RESTIC_PASSWORD }}
-          B2_ACCOUNT_ID: ${{ secrets.B2_ACCOUNT_ID }}
-          B2_ACCOUNT_KEY: ${{ secrets.B2_ACCOUNT_KEY }}