Fix Renovate config

Co-authored-by: Andrew Murray <[email protected]>

.github/renovate.json

@@ -13,5 +13,5 @@
             "separateMajorMinor": "false"
         }
     ],
-    "schedule": ["the 3rd day of the month"]
+    "schedule": ["on the 3rd day of the month"]
 }