fix: correct signer key equality checks

[overcat]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.17%. Comparing base (66e41cb) to head (da8d5f1).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1153   +/-   ##
=======================================
  Coverage   98.17%   98.17%           
=======================================
  Files         265      265           
  Lines       16532    16542   +10     
=======================================
+ Hits        16230    16240   +10     
  Misses        302      302           

Flag	Coverage Δ
unittests	98.17% <100.00%> (+<0.01%)	⬆️

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Files with missing lines	Coverage Δ
stellar_sdk/signer_key.py	95.68% <100.00%> (ø)
tests/test_signer_key.py	100.00% <100.00%> (ø)

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