Take operand constness into account in CFG construction.

[bbannier]

I looked into this since I saw a write: [i] in the CFG in #2236. This fixes a small issue, but there is definitely more we could do here.

[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #2238 will not alter performance

_{Comparing topic/bbannier/cfg-const-operands (7771551) with main (d3fe866)}

Summary

✅ 28 untouched