Use build.os instead of build.image

[babenek]

Description

Please include a summary of the change and which is fixed.

• Modification according readthedocs requirements

How has this been tested?

Please describe the tests that you ran to verify your changes.

• readthedocs build https://readthedocs.org/projects/credsweeper/builds/22288167/

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (f31f2bb) 90.77% compared to head (b0f27fb) 90.78%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #445      +/-   ##
==========================================
+ Coverage   90.77%   90.78%   +0.01%     
==========================================
  Files         125      125              
  Lines        4172     4179       +7     
  Branches      661      662       +1     
==========================================
+ Hits         3787     3794       +7     
  Misses        252      252              
  Partials      133      133              

Files	Coverage Δ
credsweeper/rules/rule.py	89.13% <100.00%> (+0.40%)	⬆️
credsweeper/scanner/scanner.py	93.69% <100.00%> (+0.11%)	⬆️

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[csh519]

I've checked the modification of ReadTheDocs.

LGTM 👍