[clang] [clang][test] Avoid writing to a potentially write-protected dir (PR #96457)

[Mariya Podchishchaeva via cfe-commits]

https://github.com/Fznamznon approved this pull request.

Whoops, sorry about that mistake in the test. The patch is LGTM. Thanks!

https://github.com/llvm/llvm-project/pull/96457