[GlobalISel][IRTranslator] Fix bit-test lowering dropping phi edges.

For contiguous ranges we drop the last bit-test case but in doing so we skip
adding the new MBB PHI edges to the list of replacement PHI edges, and as a
result we incorrectly omit them in the G_PHI in finishPendingPhis().

Was found when bootstrapping clang with -O3 and GlobalISel enabled on Apple Silicon.