[llvm] [llvm-reduce] Tighten the check to count actual store NFC (PR #210933)

[Kamlesh Kumar via llvm-commits]

kamleshbhalui wrote:

> > It was matching `store` from source test file path and test was failing.
> 
> This test has been working fine since the beginning, and has always had store in the name. Why was it failing for you?

My worktree name is `aarch64-structured-store-memoperands` It was matching `store` containing in this name.

https://github.com/llvm/llvm-project/pull/210933