[Misc] Upgrade googletest to v1.14.0

[yaox12]

Description

The current googletest is too old and has the following issues:

1. A bug in building the C++ test. See here.

In file included from /opt/dgl/dgl-source/third_party/googletest/googletest/src/gtest-all.cc:42:
/opt/dgl/dgl-source/third_party/googletest/googletest/src/gtest-death-test.cc: In function ‘bool testing::internal::StackGrowsDown()’:
/opt/dgl/dgl-source/third_party/googletest/googletest/src/gtest-death-test.cc:1291:24: error: ‘dummy’ may be used uninitialized [-Werror=maybe-uninitialized]
 1291 |   StackLowerThanAddress(&dummy, &result);
      |   ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~

2. CMake deprecation warning.

CMake Deprecation Warning at third_party/googletest/CMakeLists.txt:4 (cmake_minimum_required): 
  Compatibility with CMake < 2.8.12 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.

Checklist

Please feel free to remove inapplicable items for your PR.

• The PR title starts with [$CATEGORY] (such as [NN], [Model], [Doc], [Feature]])
• I've leverage the tools to beautify the python and c++ code.
• The PR is complete and small, read the Google eng practice (CL equals to PR) to understand more about small PR. In DGL, we consider PRs with less than 200 lines of core code change are small (example, test and documentation could be exempted).
• All changes have test coverage
• Code is well-documented
• To the best of my knowledge, examples are either not affected by this change, or have been fixed to be compatible with this change
• Related issue is referred in this PR
• If the PR is for a new model/paper, I've updated the example index here.

Changes

[dgl-bot]

To trigger regression tests:

• @dgl-bot run [instance-type] [which tests] [compare-with-branch];
  For example: @dgl-bot run g4dn.4xlarge all dmlc/master or @dgl-bot run c5.9xlarge kernel,api dmlc/master

[dgl-bot]

Commit ID: 51febfe

Build ID: 1

Status: ✅ CI test succeeded.

Report path: link

Full logs path: link