Fix CI image reference to JDK21

See gh-30339

Author: bclozel

ci/images/ci-image/Dockerfile

@@ -6,6 +6,6 @@ RUN ./setup.sh
 
 ENV JAVA_HOME /opt/openjdk/java17
 ENV JDK17 /opt/openjdk/java17
-ENV JDK21 /opt/openjdk/java20
+ENV JDK21 /opt/openjdk/java21
 
 ENV PATH $JAVA_HOME/bin:$PATH

ci/images/setup.sh

@@ -20,7 +20,7 @@ curl https://raw.githubusercontent.com/spring-io/concourse-java-scripts/v0.0.4/c
 
 mkdir -p /opt/openjdk
 pushd /opt/openjdk > /dev/null
-for jdk in java17 java20
+for jdk in java17 java21
 do
   JDK_URL=$( /get-jdk-url.sh $jdk )
   mkdir $jdk