cicd: only run lock file maintenance monthly.

Codex- · Codex- · commit edb6542ff71f · 2022-10-31T16:46:49.000+13:00
diff --git a/.github/renovate.json b/.github/renovate.json
@@ -5,7 +5,8 @@
   "labels": ["dependencies"],
   "lockFileMaintenance": {
     "enabled": true,
-    "automerge": true
+    "automerge": true,
+    "schedule": ["on the first day of the month"]
   },
   "packageRules": [
     {
