Test on ATH 21 (#11274)

Jenkinsfile

@@ -218,7 +218,7 @@ axes.values().combinations {
 
 def athAxes = [
   platforms: ['linux'],
-  jdks: [17],
+  jdks: [21],
   browsers: ['firefox'],
 ]
 athAxes.values().combinations {

ath.sh

@@ -9,7 +9,7 @@ cd "$(dirname "$0")"
 export ATH_VERSION=6433.v4d9263664552
 
 if [[ $# -eq 0 ]]; then
-	export JDK=17
+	export JDK=21
 	export BROWSER=firefox
 else
 	export JDK=$1