clang-tidy: Use cleaner path to export-fixes file with Ninja

The clang-tidy "export-fixes" flag was using unconverted Ninja paths due
to a flipped boolean check from commit 993dde925f (TargetGenerator:
Factor out generation of code check rules, 2023-05-12,
v3.27.0-rc1~84^2~2).

Source/cmCommonTargetGenerator.cxx

@@ -463,7 +463,7 @@ std::string cmCommonTargetGenerator::GenerateCodeCheckRules(
           this->GlobalCommonGenerator->AddClangTidyExportFixesFile(fixesFile);
           cmSystemTools::MakeDirectory(
             cmSystemTools::GetFilenamePath(fixesFile));
-          if (!pathConverter) {
+          if (pathConverter) {
             fixesFile = pathConverter(fixesFile);
           }
           exportFixes = cmStrCat(";--export-fixes=", fixesFile);