Update gtest used to v1.15.2

Author: mcbarton

cmake/modules/GoogleTest.cmake

@@ -17,14 +17,15 @@ if(WIN32)
     BUILD_COMMAND ${CMAKE_COMMAND} --build <BINARY_DIR> --config $<CONFIG>)
 elseif(APPLE)
   set(EXTRA_GTEST_OPTS -DCMAKE_OSX_SYSROOT=${CMAKE_OSX_SYSROOT})
+  string(REPLACE "-Wc++17-attribute-extensions" "" CMAKE_CXX_FLAGS "${CMAKE_Cxx_FLAGS}")
 endif()
 
 include(ExternalProject)
 ExternalProject_Add(
   googletest
   GIT_REPOSITORY https://github.com/google/googletest.git
   GIT_SHALLOW 1
-  GIT_TAG release-1.12.1
+  GIT_TAG v1.15.2
   UPDATE_COMMAND ""
   # # Force separate output paths for debug and release builds to allow easy
   # # identification of correct lib in subsequent TARGET_LINK_LIBRARIES commands