[Attributor][NFC] Add tests to noalias.ll

Summary: Add tests to `noalias.ll` to make changes in D84665 clear

Reviewers: jdoerfert, sstefan1, uenoku, homerdin, baziotis

Subscribers: uenoku, kuter, bbn, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D84688