Documentation: kunit: fixed sphinx error in code block

Fix a missing newline in a code block that was causing a warning:

Documentation/dev-tools/kunit/usage.rst:553: WARNING: Error in "code-block" directive:
maximum 1 argument(s) allowed, 3 supplied.

.. code-block:: bash
        modprobe example-test
Signed-off-by: Brendan Higgins <brendanhiggins@google.com>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

Documentation/dev-tools/kunit/usage.rst

@@ -551,6 +551,7 @@ options to your ``.config``:
 Once the kernel is built and installed, a simple
 
 .. code-block:: bash
+
 	modprobe example-test
 
 ...will run the tests.