Disable python bindings for Qt6

With PyQt6, sip runs into several issues, e.g.:
sip: Parser warning: /usr/lib/python3/dist-packages/PyQt6/bindings/QtCore/qnamespace.sip:53: Annotation is unknown
enum KeyboardModifier /BaseType=Flag/

sip: /usr/lib/python3/dist-packages/PyQt6/bindings/QtCore/qbytearray.sip:356: Lexical analyser error: Exactly one character expected between single quotes
QByteArray toHex(char separator /Encoding="None"/ = '\x00') const;

Author: rhaschke

src/CMakeLists.txt

@@ -3,4 +3,8 @@ add_subdirectory(image_view)
 if (CATKIN_ENABLE_TESTING)
   add_subdirectory(test)
 endif()
-add_subdirectory(python_bindings)
+if (${rviz_QT_VERSION} VERSION_LESS 6.0)
+  add_subdirectory(python_bindings)
+else()
+  message("Skipping python bindings as PyQt6 is not yet functional.")
+endif()