[FLINK-36332] Narrow down the matrix for httpclient testing.

Author: SamBarker

.github/workflows/ci.yml

@@ -78,7 +78,7 @@ jobs:
         namespace: ["default","flink"]
         mode: ["native", "standalone"]
         java-version: [ 11, 17, 21 ]
-        http-client: [ "okhttp", "vertx", "jetty",  "jdk" ]
+        http-client: [ "okhttp" ]
         test:
           - test_application_kubernetes_ha.sh
           - test_application_operations.sh
@@ -102,6 +102,12 @@ jobs:
             image: flink:1.17
           - version: v1_16
             image: flink:1.16
+          - version: v1_20
+            # Version isn't critical but should ideally be latest.
+            mode: "native"
+            namespace: "default"
+            test: test_application_operations.sh
+            http-client: [ "okhttp", "vertx", "jetty",  "jdk"]
         exclude:
           - namespace: default
             test: test_multi_sessionjob.sh