Tracking issue: rust-lang/rust#136469

Since rust-lang/rust#140172, the result of a call to any of the algebraic_add, algebraic_sub, algebraic_mul, algebraic_div, or algebraic_rem intrinsics has been deterministic in Miri.

Valid programmes do not depend on these computations being exact, thus Miri should add some non-determinism so that any such dependence is more likely to be caught.