Fix internal test failure.

test/core/security/system_roots_test.cc

@@ -93,11 +93,13 @@ TEST(CreateRootCertsBundleTest, BundlesCorrectly) {
 }
 #endif  // GPR_LINUX || GPR_FREEBSD || GPR_APPLE
 
+#if defined(GPR_WINDOWS)
 TEST(LoadSystemRootCertsTest, Success) {
   grpc_slice roots_slice = grpc_core::LoadSystemRootCerts();
   EXPECT_FALSE(GRPC_SLICE_IS_EMPTY(roots_slice));
   grpc_slice_unref(roots_slice);
 }
+#endif  // GPR_WINDOWS
 
 }  // namespace
 }  // namespace grpc