[clang] [analyzer][Solver][NFC] Cleanup const-correctness inside range-based solver (PR #112891)

[Donát Nagy via cfe-commits]

https://github.com/NagyDonat approved this pull request.

LGTM, straightforward NFC improvement. Thanks for cleaning this up!

(Currently the diff is a bit confusing, because this cleanup builds on the not-yet-merged commit https://github.com/llvm/llvm-project/pull/112887, but that's just GUI awkwardness.)

https://github.com/llvm/llvm-project/pull/112891