[FIX] test_owcsvimport: Workaround for segfault in tests on macos

[ales-erjavec]

Issue

test_owcsvimport tests sometimes segfault in CI tests.

test_browse (Orange.widgets.data.tests.test_owcsvimport.TestOWCSVFileImport) ... ok
test_browse_for_missing (Orange.widgets.data.tests.test_owcsvimport.TestOWCSVFileImport) ... Fatal Python error: Segmentation fault

Thread 0x000070000d724000 (most recent call first):
  File "/Users/runner/work/orange3-installers/orange3-installers/mnt/Orange3.app/Contents/Frameworks/Python.framework/Versions/3.10/lib/python3.10/concurrent/futures/thread.py", line 81 in _worker
  File "/Users/runner/work/orange3-installers/orange3-installers/mnt/Orange3.app/Contents/Frameworks/Python.framework/Versions/3.10/lib/python3.10/threading.py", line 953 in run
  File "/Users/runner/work/orange3-installers/orange3-installers/mnt/Orange3.app/Contents/Frameworks/Python.framework/Versions/3.10/lib/python3.10/threading.py", line 1016 in _bootstrap_inner
  File "/Users/runner/work/orange3-installers/orange3-installers/mnt/Orange3.app/Contents/Frameworks/Python.framework/Versions/3.10/lib/python3.10/threading.py", line 973 in _bootstrap

Specifically this almost always happens in the installer tests.

When build against this branch the installer tests seem to pass

Description of changes

Explicitly schedule the deletion of QFileDialog before the parent widget.

Includes

• Code changes
• Tests
• Documentation

[codecov]

Codecov Report

Merging #6735 (febf466) into master (53710be) will decrease coverage by 0.01%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6735      +/-   ##
==========================================
- Coverage   88.14%   88.13%   -0.01%     
==========================================
  Files         322      322              
  Lines       70589    70589              
==========================================
- Hits        62220    62216       -4     
- Misses       8369     8373       +4