Use Py_REFCNT instead of ob_refcnt in generated code

- ob_refcnt is not guaranteed to be there

CI: Generate wrappers for Qt 6.8

Fix build with Python 3.13 (#246)

* Fix build with Python 3.13, fixes #245
* Update build.yml to python 3.13

reintroduce the runJavaScript method on QWebEnginePage for Qt 6

albeit without the callback parameter so far

Check for duplicates at one more place

(should fix compare methods generated twice for Qt 5.12/5.15)

Add support for Qt 6.7

- use Qt 6.7 for Winodws CI build, 6.6 for ubuntu
  (jurplel/install-qt-action has a problem with that version)
- fixes #215

Allow to set and get the render API in QQuickWindow

Update generator/main.cpp

Replace deprecated include qsql.h with qtsqlglobal.h for Qt 6

Fixes #195