Configure renovate gomod every 3 months

We use dependabot as our main tool for keeping up-to-date deps. Just
keep renovate as a catch up net.

We choose to use dependabot as it provides correlation with related CVEs,
and because renovate too often fails to update go.mod (leaving raw digests in the file)

Author: jotak

renovate.json

@@ -5,9 +5,7 @@
   ],
   "labels": ["dependencies"],
   "gomod": {
-    "schedule": [
-      "after 8am on monday"
-    ],
+    "schedule": ["* * 7 */3 *"],
     "postUpdateOptions": [
       "gomodUpdateImportPaths",
       "gomodTidy",
@@ -17,11 +15,6 @@
       {
         "matchManagers": ["gomod"],
         "groupName": "Go modules"
-      },
-      {
-        "matchManagers": ["gomod"],
-        "matchUpdateTypes": ["major"],
-        "enabled": false
       }
     ]
   },