Fix loading PyKrita with PyQt 5.11
PyQt>=5.11 uses its own private copy of SIP, with sipName PyQt5.sip. This causes an API mismatch with the Krita python module, which uses the default "sip" sipName, and the module fails to load. This patch fixes this by using the PyQt5.sip sipName for PyQt>=5.11
BUG: 396381
Differential Revision: https://phabricator.kde.org/D14061