tests-pr.yml: Update the kernel and reboot before running tests
    
    This adds a couple minutes (if I read the ansible output right, it
    should be about 3 minutes) to the CI run time, but allows
    selinux-testsuite to run successfully.
    
    See also:
    https://pagure.io/fedora-ci/general/issue/162
    
    Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>