base-files: Update source code version to 10.3+deb10u4
base-files: Update source code version to 10.3+deb10u4

Change /etc/debian_version to 10.4, for Debian 10.4 point release.

Signed-off-by: Trung Do <9804f85a5a7b99b4fd74f29698e29083f5351576@toshiba.co.jp>

meta-debian/meta-debian,meta-debian/meta-debian,meta-debian/meta-debian,meta-debian/meta-debian,meta-debian/meta-debian,meta-debian/meta-debian