Simplify CI script

[wermos]

• Ninja is available by default on all runners, so there's no need to go through the hassle of manually installing it.
• The actions-setup-cmake greatly simplifies the installation of any given version of CMake, so I opted to use that instead.
• Bumped the version of actions/checkout from v3 to v4, which is the latest.
• Removed the ${{ matrix.config.cmake_args }} and ${extra_cmake_args} flags which are not used by any build configuration.
• Removed the Setup container environment as those packages are already available by default.
• Removed the Install packages step as it is not used by any build configuration.