[Core] Test core.read_model(wchar path with unicode) (openvinotoolkit#35325)

### Details:
Updated `read_model_with_const_wchar_path` in `ov_core_test.cpp` to use
the first entry from `model_files_name_w` for the model path
Follow up to openvinotoolkit#35040

### AI Assistance:
 - AI assistance used: no

---------

Co-authored-by: Pawel Raasz <pawel.raasz@intel.com>

Author: almilosz

src/inference/tests/functional/ov_core_test.cpp

@@ -192,9 +192,8 @@ TEST_F(CoreBaseTest, read_model_with_const_wchar_path) {
     generate_test_model_files("test-model");
 
     ov::Core core;
-    const std::wstring model_path_w = ov::util::string_to_wstring(model_file_name);
-    const wchar_t* model_path = model_path_w.c_str();
-    const auto model = core.read_model(model_path);
+    ASSERT_FALSE(model_files_name_w.empty());
+    const auto model = core.read_model(model_files_name_w.front().c_str());
     EXPECT_NE(model, nullptr);
 }
 #endif