[clang] [NFC]Fix memory leak in HeaderSearchTest (PR #95927)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

Thank you for the fix! FWIW, I don't think this is NFC as it is changing test behavior (fixing a memory leak); please be sure to get a proper code review for functional changes. The changes are reasonable enough, but one question I have is: why not stack allocate the object rather than heap allocate it?

https://github.com/llvm/llvm-project/pull/95927