Use error log level when contract parsing fails (#3742)

Co-authored-by: Christoph Stäbler <cstabler@redhat.com>

data-plane/core/src/main/java/dev/knative/eventing/kafka/broker/core/eventbus/ContractPublisher.java

@@ -98,7 +98,7 @@ public DataPlaneContract.Contract parseFromJson(final Reader content) throws IOE
             this.parser.merge(content, contract);
             return contract.build();
         } catch (final InvalidProtocolBufferException ex) {
-            logger.debug("failed to parse from JSON", ex);
+            logger.error("failed to parse from JSON", ex);
         }
         return null;
     }