QtSingleApplication: Fix build with Qt 6

Replace QRegExp by QRegularExpression

Change-Id: I52e997452ad7d2d14de59ad8fae597de9aec262b
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

Author: bterrier

qtsingleapplication/src/qtlocalpeer.cpp

@@ -42,6 +42,7 @@
 #include "qtlocalpeer.h"
 #include <QCoreApplication>
 #include <QDataStream>
+#include <QRegularExpression>
 #include <QTime>
 
 #if defined(Q_OS_WIN)
@@ -78,7 +79,7 @@ QtLocalPeer::QtLocalPeer(QObject* parent, const QString &appId)
 #endif
         prefix = id.section(QLatin1Char('/'), -1);
     }
-    prefix.remove(QRegExp("[^a-zA-Z]"));
+    prefix.remove(QRegularExpression("[^a-zA-Z]"));
     prefix.truncate(6);
 
     QByteArray idc = id.toUtf8();