Update modern Java to Java 25

Author: rien

dodona-java21.dockerfile

@@ -1,7 +1,7 @@
-FROM eclipse-temurin:21-jdk-alpine
+FROM eclipse-temurin:25-jdk-alpine
 
 # Install jq for json querying in bash
-RUN apk add --no-cache jq=1.8.0-r0 \
+RUN apk add --no-cache jq=1.8.1-r0 \
  # Make sure the students can't find our secret path, which is mounted in
  # /mnt with a secure random name.
  && chmod 711 /mnt \