Add decade 2020-2029 to copyright years in Checklics

Add decade 2020-2029 to copyright years in Checklics

FWIW, I just wanted to know if the tests in module 'build' would still
pass. They did not find copyrights for more recent years, so I added
them here.

But I am still unsure, if we need these tests at all. Obviously, they
were not running during CI builds, i.e. they seem to be non-essential.
But chances are, they were forgotten to be added to the suite.

BTW, running the tests in module 'build' with '-Drun.build.tests=true'
is failing, too, because some old JDK classes looked up there no longer
exist in more recent JDKs.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>