[FIX] application: Fix argparse type error

[ales-erjavec]

Issue

Ref: biolab/orange3#5927

orange-canvas raises an error with Python <= 3.7 and PyQt5 >= 5.14

...
  File "/root/DATA/orange_env/lib/python3.7/site-packages/orangecanvas/application/application.py", line 190, in argumentParser
    default=default,
  File "/usr/local/python3/lib/python3.7/argparse.py", line 1362, in add_argument
    type_func = self._registry_get('type', action.type, action.type)
  File "/usr/local/python3/lib/python3.7/argparse.py", line 1304, in _registry_get
    return self._registries[registry_name].get(value, default)
TypeError: unhashable type: 'dict'

This is due to https://bugs.python.org/issue16516

Changes

Wrap a dict.get bound method in a function.
Add test configuration that would have caught this.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 74.08%. Comparing base (5c6ccbd) to head (d90b29f).
Report is 257 commits behind head on master.

Files with missing lines	Patch %	Lines
orangecanvas/application/application.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #228      +/-   ##
==========================================
+ Coverage   74.07%   74.08%   +0.01%     
==========================================
  Files          95       95              
  Lines       20310    20312       +2     
==========================================
+ Hits        15044    15049       +5     
+ Misses       5266     5263       -3     

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