bump zombienet version (#1655)

Includes:
- fix for https://github.com/paritytech/zombienet/issues/1360 (root
cause of https://github.com/paritytech/polkadot-sdk/issues/1647)
- Improve default concurrency to spawn nodes.

Also, fix `var` name in CI file.

cc @skunert

.gitlab/pipeline/zombienet/cumulus.yml

@@ -5,7 +5,7 @@
   before_script:
     - echo "Zombie-net Tests Config"
     - echo "${ZOMBIENET_IMAGE}"
-    - echo "${RELAY_IMAGE}"
+    - echo "${POLKADOT_IMAGE}"
     - echo "${COL_IMAGE}"
     - echo "${GH_DIR}"
     - echo "${LOCAL_DIR}"