Check kernel version in Nvidia environment test

The CUDA Drivers depend on the right version of the kernel headers and development packages being installed. They in turn depend on the kernel version. Therefore kernel updates on the Ubuntu runner may require an update of the kernel headers and development packages. For more info see https://docs.nvidia.com/cuda/cuda-installation-guide-linux/index.html#pre-installation-actions.

I added a check for the kernel version to the Nvidia environment test, to make it easier to spot problems after kernel updates. It may also be useful when setting up a new machine to use this test as a reference for a working combination of Linux kernel, kernel headers, CUDA drivers and CUDA toolkit.