Issue 2895 configure isort

[PiispaH]

No functional changes, just configured isort in pyproject.toml and ran it.

Re spine-tools/Spine-Toolbox#2895

Checklist before merging

• Code has been formatted by black & isort
• Unit tests pass

[codecov]

Codecov Report

Attention: Patch coverage is 99.13420% with 2 lines in your changes missing coverage. Please review.

Project coverage is 62.36%. Comparing base (3f11246) to head (234f4ea).

Files	Patch %	Lines
...tems/data_transformer/widgets/class_tree_widget.py	0.00%	1 Missing ⚠️
.../data_transformer/widgets/parameter_tree_widget.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #217      +/-   ##
==========================================
- Coverage   62.37%   62.36%   -0.02%     
==========================================
  Files         168      168              
  Lines       17832    17826       -6     
  Branches     2979     2979              
==========================================
- Hits        11123    11117       -6     
  Misses       6104     6104              
  Partials      605      605              

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