Add missing include

This could prevent compilation in some compiler configurations.

Author: romainbrenguier

jbmc/unit/java_bytecode/java_bytecode_convert_method/convert_method.cpp

@@ -15,6 +15,7 @@ Author: Diffblue Limited.
 #include <java-testing-utils/load_java_class.h>
 #include <java-testing-utils/require_type.h>
 
+#include <goto-programs/class_hierarchy.h>
 #include <java_bytecode/java_bytecode_convert_method_class.h>
 #include <java_bytecode/java_utils.h>
 #include <testing-utils/message.h>