fix: invalid issuer error during incoming request verification if the bot host contains url parts other than the domain

[alexhook]

PR checklist

• I've written good commit message for all commits
• I've split changes into separate commits where it's appropriate
• I've added the description of function to documentation
• I've updated project version in pyproject.toml
• I'll make a release when PR is merged
• I'll bump pybotx in bot-template

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (e6d0795) to head (426acd0).

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Additional details and impacted files

@@            Coverage Diff            @@
##            master      #460   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          116       116           
  Lines         3942      3950    +8     
  Branches       347       348    +1     
=========================================
+ Hits          3942      3950    +8     

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

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