Handle dependency markers with the same name

[mrbean-bremen]

• the same name may be used in different modules
• fixes Ordering breaking with pytest-xdist + pytest-dependency #71

This came up with tests derived from a base class with dependency markers, so that all derived tests used the same alias name.

[codecov-commenter]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (19dae40) 97.21% compared to head (13651bb) 96.82%.
Report is 5 commits behind head on main.

Files	Patch %	Lines
pytest_order/sorter.py	88.46%	1 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #105      +/-   ##
==========================================
- Coverage   97.21%   96.82%   -0.40%     
==========================================
  Files           5        5              
  Lines         575      598      +23     
  Branches      136      142       +6     
==========================================
+ Hits          559      579      +20     
- Misses          9       10       +1     
- Partials        7        9       +2     

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