chore: configure renovate to run monthly (#752)

Author: enocom

.github/renovate.json

@@ -13,5 +13,8 @@
   "semanticCommits": false,
   "pip_requirements": {
     "fileMatch": ["requirements-test.txt"]
-  }
+  },
+  "schedule": [
+    "before 4am on the first day of the month"
+  ]
 }