Use dependabot to check for updates in JSON Schema test suite (#250)

Did not think that it was possible until I found the
json-schema-org/JSON-Schema-Test-Suite#549

Author: OptimumCode

.github/dependabot.yml

@@ -23,5 +23,14 @@ updates:
     assignees:
       - 'OptimumCode'
     directory: '/'
+    schedule:
+      interval: daily
+  - package-ecosystem: gitsubmodule
+    directory: "/"
+    labels:
+      - ignore
+      - tests
+    assignees:
+      - 'OptimumCode'
     schedule:
       interval: daily