OpenJDK 13 (ea) entering testing

[Matthias Klose <doko@debian.org>]

The next OpenJDK LTS will be OpenJDK 17, to be released in September/October
2021.  So we will stay with OpenJDK 11 for bullseye.  However we should start
testing packages using the interim versions, or else we'll have again one big
version bump from 11 to 17.  To get a bit more exposure of these interim
versions, I'll let these migrate to testing, and to have a safer fallback if
packages get accidentally removed from unstable.  OpenJDK 12 will be removed
from unstable soonish, because it won't see the next round of security updates
anymore later this month.

Please stay away from backporting these interim versions to stable backports.

Would anybody be interested in setting up a machine to check builds with interim
OpenJDK versions?

Thanks, Matthias