Update to jdk-21.0.11 --- second attempt!

[Makarius]

On 02/06/2026 21:10, Makarius wrote:
> With Isabelle/895b651beabb we are on jdk-21.0.11, which alone is not very 
> exciting: it is a routine update by Azul.

Another side-remark: We are still on the old JDK 21 LTS branch because we are 
stuck with an old Scala LTS version scala-3.3.4 from Sep-2024 that has not 
been adapted to newer JDK versions yet, like the current JDK 25 LTS.

After scala-3.3.4 there is a problem with inner Java classes that are 
extended/redefined in Scala. I have submitted a ticket in Nov-2025 
https://github.com/scala/scala3/issues/24507 --- that is still awaiting to be 
shipped in a proper LTS release. The last one is scala-3.3.7 from 13-Oct-2025.


	Makarius