Ignore errors for sip with no setapi.

Apparently, this happens (see matplotlib#20040 and related issues) sporadically.
We don't care if we can't change the sip API version (if it's already
been set), so also stop caring if the `setapi` function doesn't exist.
This should simply cause the Qt4 backend to fail correctly later with an
`ImportError` instead, and thus fall back to the next backend candidate.

Fixes matplotlib#20040.

Author: QuLogic

lib/matplotlib/backends/qt_compat.py

@@ -117,7 +117,7 @@ def _setup_pyqt4_internal(api):
             for _sip_api in _sip_apis:
                 try:
                     sip.setapi(_sip_api, api)
-                except ValueError:
+                except (AttributeError, ValueError):
                     pass
         from PyQt4 import QtCore, QtGui
         import sip  # Always succeeds *after* importing PyQt4.