Fix The annoyning Deprecation issue in _middlewares.py

[ahmed-ellaban]

This pull request includes a change to the slot_request method in the scrapy_zyte_api/_middlewares.py file. The change involves modifying the way the slot key is obtained from the downloader.

• scrapy_zyte_api/_middlewares.py: Changed the method call from downloader._get_slot_key(request, spider) to downloader.get_slot_key(request) to use the public method instead of a private one, and hide the warning log

Fixes #232

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.89%. Comparing base (5fbf0bc) to head (bacc5ed).
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #234   +/-   ##
=======================================
  Coverage   97.89%   97.89%           
=======================================
  Files          14       14           
  Lines        1615     1618    +3     
  Branches      297      297           
=======================================
+ Hits         1581     1584    +3     
  Misses         14       14           
  Partials       20       20           

Files with missing lines	Coverage Δ
scrapy_zyte_api/_middlewares.py	97.65% <100.00%> (+0.05%)	⬆️

[wRAR]

Thanks!