[NFC][LoopUnroll] Add `-unroll-runtime-other-exit-predictable=false` in

`runtime-multiexit-heuristic.ll`

Added -unroll-runtime-other-exit-predictable=false in
runtime-multiexit-heuristic.ll to make it more robust.
runtime-multiexit-heuristic.ll intention is to test
-unroll-runtime-multi-exit=false, so the default value of
-unroll-runtime-other-exit-predictable should not impact the result.

Reviewed By: Meinersbur

Differential Revision: https://reviews.llvm.org/D98098