Fix a few certificates

[cffls]

Fix a few certificates and make integration test more stable.

[codecov]

Codecov Report

Attention: Patch coverage is 95.23810% with 1 line in your changes missing coverage. Please review.

Project coverage is 88.03%. Comparing base (ba35e9c) to head (f69ddd5).

Files with missing lines	Patch %	Lines
pycardano/certificate.py	92.85%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #423      +/-   ##
==========================================
+ Coverage   84.55%   88.03%   +3.47%     
==========================================
  Files          31       32       +1     
  Lines        4429     4513      +84     
  Branches     1131     1150      +19     
==========================================
+ Hits         3745     3973     +228     
+ Misses        538      380     -158     
- Partials      146      160      +14     

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