Fix typo in the expression

Co-authored-by: Alexander M. Turek <me@derrabus.de>

doctrine.rst

@@ -999,7 +999,7 @@ In addition, you can query directly with SQL if you need to::
                 ORDER BY p.price ASC
                 ';
 
-            $resultSet = $stmt->executeQuery($sql, ['price' => $price]);
+            $resultSet = $conn->executeQuery($sql, ['price' => $price]);
 
             // returns an array of arrays (i.e. a raw data set)
             return $resultSet->fetchAllAssociative();