remove parallel requests branch test

[beliaev-maksim]

basically, we always run on the same version of requests. Just remove redundant pipeline.

if in some time requests 3.X will come, we can update. So far requests 3 project is frozen and is not updated since 4 years.

Even if it will come, we will need to test it first, before releasing to wider audience. Thus, fix requests version in setup.py

[codecov]

Codecov Report

Merging #473 (4f0103c) into master (a552398) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #473   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            5         5           
  Lines         2026      2026           
=========================================
  Hits          2026      2026           

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