Silence redocly-cli rule checking examples

`$ref` inside examples is non-compliant for OpenAPI / Json Schema, so
this rule fails to check the examples properly.

We already perform this check with
`scripts/check-event-schema-examples.py`.

Signed-off-by: Kévin Commaille <zecakeh@tedomum.fr>

redocly.yaml

@@ -9,3 +9,5 @@ rules:
   no-path-trailing-slash: off
   operation-2xx-response: off
   spec-strict-refs: error
+  # $ref in examples are not spec-compliant so we perform this check in a python script.
+  no-invalid-schema-examples: off