Fix naming for incrementing and decrementing balance in transfer function

[FredCoen]

I think there was a naming confusion here. Fixed it with using decr for decremented balance and incr for incremented balance.

[codspeed-hq]

CodSpeed Performance Report

Merging #1976 will not alter performance

_{Comparing FredCoen:correct-variable-naming (e03de47) with main (04688b7)}

Summary

✅ 8 untouched benchmarks

[rakita]

makes sense