[clang-tools-extra] [clang-doc] switched from using relative to absolute paths (PR #93281)

[via cfe-commits]

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@@ -0,0 +1,7 @@
+// RUN: rm -rf %t && mkdir %t
+// RUN: cp "%s" "%t/test.cpp"
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PeterChou1 wrote:

Sorry, the reason why I kept using this pattern is because I copied the same test setups in the original test for clang-doc [here](https://github.com/llvm/llvm-project/blob/main/clang-tools-extra/test/clang-doc/single-file.cpp#L4) and [here](https://github.com/llvm/llvm-project/blob/main/clang-tools-extra/test/clang-doc/single-file-public.cpp#L4)

https://github.com/llvm/llvm-project/pull/93281