Eliminate compilation warnings

When converting a const variable to a non-const variable, use the conversion operator　

Change-Id: Ib1c8f3defbf9ccce1af5c90e7e9c508bc8c039d0
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
Reviewed-by: Paul Wicking <paul.wicking@qt.io>

src/corelib/text/qstring.cpp

@@ -7644,7 +7644,7 @@ static QString replaceArgEscapes(QStringView s, const ArgEscapeData &d, int fiel
                      *qMax(abs_field_width, larg.length());
 
     QString result(result_len, Qt::Uninitialized);
-    QChar *result_buff = (QChar*) result.unicode();
+    QChar *result_buff = const_cast<QChar *>(result.unicode());
 
     QChar *rc = result_buff;
     const QChar *c = uc_begin;