[InstCombine] Fix worklist management in select fold (#77738)

`InstCombine` uses `Worklist` to manage change history. `setOperand`,
which was previously used to change the `Select` Instruction, does not,
so it is `run` twice, which causes an `LLVM ERROR`.

This problem is resolved by changing `setOperand` to `replaceOperand` as
the change history will be registered in the Worklist.

Fixes #77553.