Change the base docker image in the broker topology.

Set the version of the base docker image to 3.4.8-almalinux8.

Change-Id: Id086eecf1f9206b3c3286ac0ad3cb103c8922d4b
diff --git a/example-setup/broker/Dockerfile b/example-setup/broker/Dockerfile
index abc12cf..df097d8 100644
--- a/example-setup/broker/Dockerfile
+++ b/example-setup/broker/Dockerfile
@@ -1,4 +1,4 @@
-FROM gerritcodereview/gerrit:3.5.4-almalinux8
+FROM gerritcodereview/gerrit:3.4.8-almalinux8
 
 USER root