MAINTAINERS: Update KUnit email address for Brendan Higgins

Update Brendan's email address for the KUnit entry.

Link: https://lore.kernel.org/r/20241115050510.56569-1-brendanhiggins@google.com


Signed-off-by: Brendan Higgins <brendanhiggins@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>