kbuild: deb-pkg: add python3:native to build dependency

Python3 is necessary for running some scripts such as
drivers/gpu/drm/msm/registers/gen_header.py

Both scripts/package/kernel.spec and scripts/package/PKGBUILD already
list Python as the build dependency.

Do likewise for scripts/package/mkdebian.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

scripts/package/mkdebian

@@ -202,7 +202,7 @@ Build-Depends-Arch: bc, bison, cpio, flex,
  gcc-${host_gnu} <!pkg.${sourcename}.nokernelheaders>,
  kmod, libelf-dev:native,
  libssl-dev:native, libssl-dev <!pkg.${sourcename}.nokernelheaders>,
- rsync
+ python3:native, rsync
 Homepage: https://www.kernel.org/
 
 Package: $packagename-$version