Use Java 21 for the Gerrit image

As mentioned in the Gerrit v3.11 release notes at [1], the
artifacts are built by default with Java 21, therefore the CI
jars won't be compatible at runtime with Java 17 anymore.

[1] https://www.gerritcodereview.com/3.11.html#java-21

Change-Id: I30f48239dec8de3e8fb645fbfeba71dab85da9fa

src/test/docker/gerrit/Dockerfile

diff --git a/src/test/docker/gerrit/Dockerfile b/src/test/docker/gerrit/Dockerfile
index 6e0d639..f082d2f 100644
--- a/src/test/docker/gerrit/Dockerfile
+++ b/src/test/docker/gerrit/Dockerfile
@@ -3,7 +3,7 @@
 # Install dependencies
 RUN yum -y install \
     git \
-    java-17-openjdk \
+    java-21-openjdk \
     procps \
     sudo \
     passwd \