[clang][deps] Fix test by checking ignored files correctly

After a rebase, bc1a297 accidentally changed `shouldIgnoreFile(Filename)` to incorrect `IgnoredFiles.count(Filename)`. This avoided using native filenames, which the patch intended to solve in the first place.

Failing Windows builds:
* https://lab.llvm.org/buildbot#builders/123/builds/5147
* https://lab.llvm.org/buildbot#builders/86/builds/17177

clang/lib/Tooling/DependencyScanning/DependencyScanningFilesystem.cpp

@@ -166,8 +166,7 @@ bool DependencyScanningWorkerFilesystem::shouldIgnoreFile(
 llvm::ErrorOr<const CachedFileSystemEntry *>
 DependencyScanningWorkerFilesystem::getOrCreateFileSystemEntry(
     const StringRef Filename) {
-  bool ShouldMinimize =
-      !IgnoredFiles.count(Filename) && shouldMinimize(Filename);
+  bool ShouldMinimize = !shouldIgnoreFile(Filename) && shouldMinimize(Filename);
 
   if (const auto *Entry = Cache.getCachedEntry(Filename, ShouldMinimize))
     return Entry;