[llvm] [CAS] Close the stderr temp file of the out-of-process validator (PR #226844)

[Dmitry Vasilyev via llvm-commits]

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@@ -0,0 +1,7 @@
+RUN: rm -rf %t
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slydiman wrote:

I think `rm -rf %t` is too much.
`rm -rf %t %t/cas` must be enough and more safer.

https://github.com/llvm/llvm-project/pull/226844