MariaDB 10.3 test packages should be removed from experimental. I think it was just a temporary test by Ondrej. There is no point in having a unreleased upstream version in Debian permantently.
- Bug#863675: libmariadbd-dev: fails to upgrade from 'sid'... Andreas Beckmann
- Bug#863675: [debian-mysql] Bug#863675: libmariadbd-... Otto Kekäläinen
- Bug#863675: [debian-mysql] Bug#863675: Bug#8636... Robie Basak
- Bug#863675: [debian-mysql] Bug#863675: Bug#... Ondřej Surý