Set Java version to 1.8 to match Maven build.

[sebastic]

Not setting the version results in much too high bytecode version to be used which complicates compatibility with reverse dependencies like osmosis.

[leonardehrenfried]

In 15 years of writing Java I have never used ant so I have no idea if this is correct, but it looks fine to me.

Question: do you need a deployment to Maven Central for this? Presumably not, because ant doesn't use Maven Central, correct?

[sebastic]

In 15 years of writing Java I have never used ant so I have no idea if this is correct, but it looks fine to me.

It's correct per the documentation: https://ant.apache.org/manual/Tasks/javac.html

And also fixes the issue with the Debian package that blocked testing migration:

https://qa.debian.org/excuses.php?package=osmpbf

Question: do you need a deployment to Maven Central for this?

No, the osmpbf Debian package uses the ant build because it's so much simpler than Maven.

Presumably not, because ant doesn't use Maven Central, correct?

Indeed.