Re-introduce support for QMatrix when building against Qt < 6.0

This partially reverts 10a3e49 ("Qt6 compatibility fixes for core
PythonQt library", 2023-08-21)

Author: jcfr

src/PythonQt.cpp

@@ -260,6 +260,9 @@ void PythonQt::init(int flags, const QByteArray& pythonQtModuleName)
     PythonQtRegisterToolClassesTemplateConverterForKnownClass(QPen);
     PythonQtRegisterToolClassesTemplateConverterForKnownClass(QTextLength);
     PythonQtRegisterToolClassesTemplateConverterForKnownClass(QTextFormat);
+#if QT_VERSION < 0x060000
+    PythonQtRegisterToolClassesTemplateConverterForKnownClass(QMatrix);
+#endif
 
     PyObject* pack = PythonQt::priv()->packageByName("QtCore");
     PyObject* pack2 = PythonQt::priv()->packageByName("Qt");

src/PythonQtVariants.h

@@ -72,6 +72,9 @@
 #include <QPen>
 #include <QTextLength>
 #include <QTextFormat>
+#if QT_VERSION < 0x060000
+#include <QMatrix>
+#endif
 
 #endif