Bug fix and clean pytest.ini

[zhiwei2017]

1. fixed issue, where the package is incompatible with python 3.8 due to changed signature of function get_mixins in class EnumMeta. (Closes Incompatible with Python 3.8 #66)
2. merged pytest.ini into setup.cfg

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[codecov-commenter]

Codecov Report

Merging #67 (410beb8) into dev (81452eb) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##               dev       #67   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines          167       170    +3     
=========================================
+ Hits           167       170    +3     

Impacted Files	Coverage Δ
named_enum/__init__.py	100.00% <100.00%> (ø)

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