Add scheduled workflow run deletion (JabRef#12714)

Author: koppor

.github/workflows/delete-old-runs-automatically.yml

@@ -0,0 +1,18 @@
+name: Delete old workflow runs (automatically)
+on:
+  schedule:
+    - cron: '0 0 1 * *'
+jobs:
+  del_runs:
+    runs-on: ubuntu-latest
+    permissions:
+      actions: write
+      contents: read
+    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

.github/workflows/delete-old-runs.yml renamed to .github/workflows/delete-old-runs-manually.yml

@@ -1,4 +1,4 @@
-name: Delete old workflow runs
+name: Delete old workflow runs (manually)
 on:
   workflow_dispatch:
     inputs: