Fix deserialization of certificates

[nielstron]

This fixes deserializing transactions that contain a list of certificates (or more specifically, fixes certificate deserialization from cbor)

[codecov-commenter]

Codecov Report

Attention: 18 lines in your changes are missing coverage. Please review.

Comparison is base (b2d74cc) 83.11% compared to head (6171067) 82.88%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
pycardano/certificate.py	56.75%	9 Missing and 7 partials ⚠️
pycardano/txbuilder.py	33.33%	2 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #310      +/-   ##
==========================================
- Coverage   83.11%   82.88%   -0.24%     
==========================================
  Files          28       28              
  Lines        3441     3476      +35     
  Branches      844      865      +21     
==========================================
+ Hits         2860     2881      +21     
- Misses        430      438       +8     
- Partials      151      157       +6     

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[nielstron]

I think this has been scooped by #321