refactor(tests): modernize CMake configuration for notification server tests

Replaced global CMAKE_CXX_FLAGS with target-specific compile options
using target_compile_options() for better encapsulation.
Removed redundant include(GoogleTest) since find_package(GTest) is already called.

Log: Modernize CMake configuration for notification server tests

Influence:
1. Verify notifyserverapplet_tests builds successfully
2. Confirm no CMake configuration warnings

refactor(tests): 现代化通知服务器测试的 CMake 配置

使用 target_compile_options() 替代全局 CMAKE_CXX_FLAGS，
提供更好的封装性。移除冗余的 include(GoogleTest)。

Log: 现代化通知服务器测试的 CMake 配置

Influence:
1. 验证 notifyserverapplet_tests 构建成功
2. 确认没有 CMake 配置警告

Author: heysion

tests/panels/notification/server/CMakeLists.txt

@@ -5,7 +5,7 @@
 find_package(GTest REQUIRED)
 find_package(Qt${QT_VERSION_MAJOR} ${REQUIRED_QT_VERSION} REQUIRED COMPONENTS Core Test DBus)
 
-include(GoogleTest)
+find_package(GTest REQUIRED)
 
 add_executable(notifyserverapplet_tests
     ${CMAKE_SOURCE_DIR}/panels/notification/server/notifyserverapplet.h
@@ -28,7 +28,7 @@ add_executable(notifyserverapplet_tests
     notifyserverapplet_test.cpp
 )
 
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fvisibility=hidden -fvisibility-inlines-hidden")
+target_compile_options(notifyserverapplet_tests PRIVATE -fvisibility=hidden -fvisibility-inlines-hidden)
 
 target_link_libraries(notifyserverapplet_tests PRIVATE
     GTest::GTest