Fix executemany with binary prefix

[methane]

Fix #494

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.04 ⚠️

Comparison is base (3517eb7) 88.90% compared to head (a7c27c5) 88.86%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #605      +/-   ##
==========================================
- Coverage   88.90%   88.86%   -0.04%     
==========================================
  Files           7        7              
  Lines         568      548      -20     
==========================================
- Hits          505      487      -18     
+ Misses         63       61       -2     

Impacted Files	Coverage Δ
src/MySQLdb/cursors.py	86.29% <100.00%> (-0.28%)	⬇️

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