Avoid more uses of non-explicit QChar(int) constructor

Will be gone in Qt6.

Task-number: QTCREATORBUG-24098
Change-Id: Id76b15bb11879b2e8ff0f71af45acbfb1720f763
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/libs/qmljs/parser/qmljslexer.cpp

@@ -986,7 +986,7 @@ int Lexer::scanString(ScanStringMode mode)
                     _tokenText += QChar(QChar::highSurrogate(codePoint));
                     u = QChar::lowSurrogate(codePoint);
                 } else {
-                    u = codePoint;
+                    u = QChar(codePoint);
                 }
             } break;