Consider to update gtest to newer version

[mikir]

We are currently using gtest version 1.11.0 from Jun 2021.

It would be good to update it to newer version. However, we have observed some compilation problems on some MinGW distributions using new version 1.12.0. This should be investigated and clarified.

Beside of that, the version 1.12.0 is the last one which still supports C++11.

The main problem of old gtest version 1.11.0 is the following cmake warning:

CMake Deprecation Warning at /home/runner/work/zserio/zserio/3rdparty/cpp/googletest/CMakeLists.txt:4 (cmake_minimum_required):
  Compatibility with CMake < 3.5 will be removed from a future version of
  CMake.
  Update the VERSION argument <min> value or use a ...<max> suffix to tell
  CMake that the project does not need compatibility with older versions.
CMake Deprecation Warning at /home/runner/work/zserio/zserio/3rdparty/cpp/googletest/googletest/CMakeLists.txt:56 (cmake_minimum_required):
  Compatibility with CMake < 3.5 will be removed from a future version of
  CMake.
  Update the VERSION argument <min> value or use a ...<max> suffix to tell
  CMake that the project does not need compatibility with older versions.

The problem above could be a potential problem in the future.