kernel-devsrc: depend on python3-core instead of python3

Avoids pulling in potential GPLv3 packages through python3-misc catch-all.

python3-core is the intended minimal RDEPENDS for packages requiring python3
support.  Other python3 module dependencies should be listed explicitly.

Signed-off-by: Kyle Russell <bkylerussell@gmail.com>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
(cherry picked from commit 231f93be)
Signed-off-by: Steve Sakoman <steve@sakoman.com>