fix json/gis/text/blob meta response inconsistent with mysql5.7 （master）

src/sql/ob_result_set.cpp

@@ -1724,6 +1724,9 @@ void ObResultSet::replace_lob_type(const ObSQLSessionInfo &session,
       // for 5.x, always return MYSQL_TYPE_BLOB
       // for 8.x always return MYSQL_TYPE_BLOB, and do text type judge in mysql-jdbc by length
       mfield.type_ = obmysql::EMySQLFieldType::MYSQL_TYPE_BLOB;
+    } else if (mfield.type_ == obmysql::EMySQLFieldType::MYSQL_TYPE_JSON) {
+      // for mysql 5.x json response as plain text not binary, but the charset always binary
+      mfield.charsetnr_ = common::CS_TYPE_BINARY;
     }
   }
 }