Update mariadb version in sid.

Signed-off-by: Andrew Lee (李健秋) ajqlee@debian.org

mariadb-server-10.3 is not in Buster...

$ rmadison mariadb-server-10.3
mariadb-server-10.3 | 1:10.3.12-1   | unstable        | kfreebsd-i386, mips64el
mariadb-server-10.3 | 1:10.3.12-2   | buildd-unstable | amd64, arm64, armel, armhf, hurd-i386, i386, mips, mipsel, ppc64el, s390x
mariadb-server-10.3 | 1:10.3.12-2   | unstable        | amd64, arm64, armel, armhf, hurd-i386, i386, mips, mipsel, ppc64el, s390x

But this is for the sid images. Not for buster.

mentioned in commit 31d38e3c

merged