Kokoro changes:
- Linux: gcc-13, cmake-3.31.2
- Windows: python 3.12, cmake-3.31.2
* Disable warnings in gtest, gmock
This is required in order to build with GCC 13, and Apple Clang with warnings-as-errors
Bug: crbug.com/383538610
* disable license check on .github/workflows/main.yml
* Use add_subdirectory for internal gtest, gmock
---------
Co-authored-by: Antonio Maiorano <amaiorano@google.com>
`license-checker` is a tool that verifies each file has contains a permitted license header.
See https://github.com/ben-clayton/license-checker for more information.
Also add missing licenses to presubmit scripts.
