[ConstraintElimination] Only add cond from assume to succs if valid.

[ConstraintElimination] Only add cond from assume to succs if valid.

Add missing CanAdd check before adding a condition from an assume
to the successor blocks. When adding information from assume to
successor blocks we need to perform the same CanAdd as we do for adding
a condition from a branch.

Fixes https://github.com/llvm/llvm-project/issues/54217