Fix handling of collections by non-reactive Consumers

Author: olegz

spring-cloud-function-context/src/main/java/org/springframework/cloud/function/context/catalog/SimpleFunctionRegistry.java

@@ -815,6 +815,9 @@ private Map<String, Object> sanitizeHeaders(MessageHeaders headers) {
 		 */
 		@SuppressWarnings("unchecked")
 		private Object fluxifyInputIfNecessary(Object input) {
+			if (input instanceof Message && !((Message) input).getHeaders().containsKey("user-agent") && this.isConsumer() && !this.isInputTypePublisher()) {
+				return input;
+			}
 			if (FunctionTypeUtils.isMultipleArgumentType(this.inputType)) {
 				return input;
 			}