[clang] [clang-tools-extra] [clang-format][clang-tools-extra] Fix leaking of host-level config into test environment (PR #206358)

[Baranov Victor via cfe-commits]

================
@@ -63,10 +63,10 @@ class ChangeNamespaceTest : public ::testing::Test {
   }
 
 protected:
-  std::string FileName = "input.cc";
+  std::string FileName = "/test/input.cc";
----------------
vbvictor wrote:

In other words, how it previously failed due to .clang-format?
clang-change-namespaces seems a complete separate tool to me

https://github.com/llvm/llvm-project/pull/206358