Update googletest version

What is the new feature

Update googletest version. The old v1.12.1 uses a deprecated CMake minimum version.

How is it implemented

Update the download version in FetchContent

Mandatory steps before review

• Gitlab CI passes (Hint: use make format for linting)
• New feature is covered by additional unit tests
• Mark the merge request as ready by removing Draft:

Mandatory steps before merge

• Reviewed by a maintainer
• Incorporate review suggestions
• Remember to edit the commit message and select the proper changelog category (feature/bugfix/other)
• Prior to merging, please remove any boilerplate from the MR description, retaining only the Please describe your feature in a couple of words and describe important implementation details of the feature section to maintain

You are not supposed to merge this request by yourself, the maintainers of libiconmath take care of this action!

test/c/CMakeLists.txt

@@ -10,13 +10,18 @@
 # ---------------------------------------------------------------
 
 # Fetch GoogleTest via FetchContent
+message(CHECK_START "Fetching external googletest")
+if("${CMAKE_VERSION}" VERSION_GREATER_EQUAL "3.24")
+  cmake_policy(SET CMP0135 NEW)
+endif()
 include(FetchContent)
 FetchContent_Declare(
   googletest
-  URL https://github.com/google/googletest/archive/refs/tags/release-1.12.1.zip
+  URL https://github.com/google/googletest/releases/download/v1.16.0/googletest-1.16.0.tar.gz
 )
 # set(gtest_force_shared_crt ON CACHE BOOL "" FORCE)
 FetchContent_MakeAvailable(googletest)
+message(CHECK_PASS "done")
 
 # Find Kokkos (or use your existing Kokkos installation)
 # find_package(Kokkos REQUIRED)