[FIX] widgettoolbox: Fix WidgetToolBox tests with Python 3.12

[ales-erjavec]

Issue

Running unittests on Python 3.12 aborts with

...
test_filter (orangecanvas.application.tests.test_widgettoolbox.TestWidgetToolBox.test_filter) ... ok
Traceback (most recent call last):
  File "/home/ales/devel/orange-canvas-core/orangecanvas/application/widgettoolbox.py", line 161, in actionEvent
    button = self.buttonForAction(event.action())
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ales/devel/orange-canvas-core/orangecanvas/gui/toolgrid.py", line 345, in buttonForAction
    index = actions.index(action)
            ^^^^^^^^^^^^^^^^^^^^^
ValueError: <PyQt6.QtGui.QAction object at 0x7fd2b44b48a0> is not in list
Fatal Python error: Aborted

Changes

Handle model reset and use model reset in test tearDown to avoid errors in tests.

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (7f535af) 75.47% compared to head (1ecdf6d) 75.67%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #283      +/-   ##
==========================================
+ Coverage   75.47%   75.67%   +0.20%     
==========================================
  Files          99       99              
  Lines       21033    21043      +10     
==========================================
+ Hits        15875    15925      +50     
+ Misses       5158     5118      -40     

Files	Coverage Δ
orangecanvas/application/widgettoolbox.py	74.44% <91.66%> (+0.51%)	⬆️

... and 5 files with indirect coverage changes

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