update version of gtest to v1.15.2 (latest) and also the cmake config (#1864)

* update version of gtest to v1.15.2 (latest) and also the cmake configuration to avoid deprecation warnings

* `cmake/GoogleTest.cmake.in`: do a shallow clone of google test

---------

Co-authored-by: dominic <[email protected]>
Co-authored-by: Roman Lebedev <[email protected]>

Author: 3 people

cmake/GoogleTest.cmake.in

@@ -34,11 +34,12 @@ else()
     message(SEND_ERROR "Did not find Google Test sources! Either pass correct path in GOOGLETEST_PATH, or enable BENCHMARK_DOWNLOAD_DEPENDENCIES, or disable BENCHMARK_USE_BUNDLED_GTEST, or disable BENCHMARK_ENABLE_GTEST_TESTS / BENCHMARK_ENABLE_TESTING.")
     return()
   else()
-    message(WARNING "Did not find Google Test sources! Fetching from web...")
+    message(STATUS "Did not find Google Test sources! Fetching from web...")
     ExternalProject_Add(
       googletest
       GIT_REPOSITORY    https://github.com/google/googletest.git
-      GIT_TAG           "v1.14.0"
+      GIT_TAG           "v1.15.2"
+      GIT_SHALLOW       "ON"
       PREFIX            "${CMAKE_BINARY_DIR}"
       STAMP_DIR         "${CMAKE_BINARY_DIR}/stamp"
       DOWNLOAD_DIR      "${CMAKE_BINARY_DIR}/download"