Run JDK 21 workflows with latest JDK.

[gianm]

Reverts PR #17458. There's a new JDK out (21.0.6). Hopefully it does not segfault.

[gianm]

JDK21 processing tests passed (yay). I re-ran them to be sure.

[kgyrtkirk]

I've just seen this: https://github.com/apache/druid/actions/runs/13161729196/job/36736492139?pr=17699

seems like the issue is still present; we should probably revert this.

console log snipplet

 #
# A fatal error has been detected by the Java Runtime Environment:
#
#  SIGSEGV (0xb) at pc=0x00007f1ae1b0f659, pid=7302, tid=8432
#
# JRE version: OpenJDK Runtime Environment Zulu21.40+17-CA (21.0.6+7) (build 21.0.6+7-LTS)
# Java VM: OpenJDK 64-Bit Server VM Zulu21.40+17-CA (21.0.6+7-LTS, mixed mode, sharing, tiered, compressed oops, compressed class ptrs, g1 gc, linux-amd64)
# Problematic frame:
# V  [libjvm.so+0xf0f659]  BoolNode::Ideal(PhaseGVN*, bool)+0x19
#
# Core dump will be written. Default location: Core dumps may be processed with "/usr/lib/systemd/systemd-coredump %P %u %g %s %t 9223372036854775808 %h" (or dumping to /home/runner/work/druid/druid/indexing-service/core.7302)
#
# JFR recording file will be written. Location: /home/runner/work/druid/druid/indexing-service/hs_err_pid7302.jfr
#
# An error report file with more information is saved as:
# /home/runner/work/druid/druid/indexing-service/hs_err_pid7302.log
#
# Compiler replay data is saved as:
# /home/runner/work/druid/druid/indexing-service/replay_pid7302.log

[Akshat-Jain]

Another one: https://github.com/apache/druid/actions/runs/13171860722/job/36765570030?pr=17653