The man page says that --sign-kernel and --no-sign-kernel "override the
detection of whether to sign the Linux binary", so we should only
autodetect if neither are specified. But as of commit 02eabaffe9
("ukify: Add a unified interface for signing tools"), we autodetect even
when --no-sign-kernel is passed, which makes the flag useless.
The sign_kernel option is parsed using argparse.BooleanOptionalAction,
which sets it to either True, False, or None. commit 02eabaffe9
replaced `sign_kernel is None` with `not sign_kernel`. These are not the
same in Python, as the latter accepts False as well as None.
Restore the original check and fix type annotations accordingly.
Fixes: 02eabaffe9 ("ukify: Add a unified interface for signing tools")