Bump Zookeeper image version in tests (#563)

# Description

*Please add a description here. This will become the commit message of the merge request later.*

Author: sbernauer

tests/test-definition.yaml

@@ -11,12 +11,12 @@ dimensions:
       - 3.3.1-stackable23.4.0-rc2
   - name: zookeeper
     values:
-      - 3.6.3-stackable23.4.0-rc1
-      - 3.7.0-stackable23.4.0-rc1
-      - 3.8.0-stackable23.4.0-rc1
+      - 3.6.3-stackable23.4.0-rc2
+      - 3.7.0-stackable23.4.0-rc2
+      - 3.8.0-stackable23.4.0-rc2
   - name: zookeeper-latest
     values:
-      - 3.8.0-stackable23.4.0-rc1
+      - 3.8.0-stackable23.4.0-rc2
   - name: upgrade_old
     values:
       - 2.8.1-stackable23.4.0-rc2