jtreg7: request to vendor the dependencies

Hi,

jtreg7 is a package that provides regression testing for openjdk-21
and soon openjdk-17 and is critical to the openjdk package build
process.

jtreg7 depends on a number of test-related packages (junit4, junit5,
libhamcrest-java) that require transitive dependencies such as picocli
or opentest4j-reporting either introduced (that is not an issue) or
upgraded.

A new point release of the package in the stable release requires
careful testing and ensuring that there is no impact on reverse
dependencies.

JTreg is seeing some acceleration in development and will require a
regular backporting effort for the dependencies.

I wonder if it is possible to provide an exclusion for jtreg7 to
vendor the required dependencies to simplify the backporting effort.

The draft vendoring implementation is available here[1].

Best Regards,
 Vladimir.

[1] https://salsa.debian.org/vpa1977/jtreg/-/commit/eebacdae191d6f0a833d548681fb3fe6b17dbd91