Fix Unchecked Compiler Warning

Author: garyrussell

spring-kafka/src/main/java/org/springframework/kafka/support/KafkaMessageHeaderAccessor.java

@@ -77,6 +77,7 @@ private int fromBytes(String headerName) {
 	 * @return the value, if present.
 	 * @throws IllegalArgumentException if the type is not correct.
 	 */
+	@SuppressWarnings("unchecked")
 	@Nullable
 	public <T> T getHeader(String key, Class<T> type) {
 		Object value = getHeader(key);