[clang][deps] Fix test after upstream change NFC

After the -working-directory fix, this test needs to use a relative path
for "ReadFiles". Note: This test already used a relative path upstream,
but was modified downstream.

(cherry picked from commit 64a0b07)

Author: benlangmuir

clang/unittests/Tooling/DependencyScannerTest.cpp

@@ -355,5 +355,5 @@ TEST(DependencyScanner, ScanDepsWithModuleLookup) {
 
   EXPECT_TRUE(llvm::find(InterceptFS->StatPaths, OtherPath) ==
               InterceptFS->StatPaths.end());
-  EXPECT_EQ(InterceptFS->ReadFiles, std::vector<std::string>{"/root/test.m"});
+  EXPECT_EQ(InterceptFS->ReadFiles, std::vector<std::string>{"test.m"});
 }