deps: use xdrlib3 instead of xdrlib.

[overcat]

xdrlib will be removed in Python 3.13.

#646

[codecov]

Codecov Report

Merging #739 (978cca0) into main (4286734) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #739   +/-   ##
=======================================
  Coverage   99.25%   99.25%           
=======================================
  Files         233      233           
  Lines       11334    11334           
=======================================
+ Hits        11249    11250    +1     
+ Misses         85       84    -1     

Flag	Coverage Δ
unittests	99.25% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
stellar_sdk/fee_bump_transaction_envelope.py	95.45% <100.00%> (ø)
stellar_sdk/strkey.py	99.37% <100.00%> (ø)
stellar_sdk/transaction_envelope.py	97.26% <100.00%> (ø)

... and 1 file with indirect coverage changes