test both 10.X and 9.X splunk versions

Author: Kawron

.github/workflows/ci_build_test.yaml

@@ -128,6 +128,11 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
+        splunk:
+          - splunk_version: "10.0.0"
+            splunk_filename: "splunk-10.0.0-e8eb0c4654f8-linux-amd64.tgz"
+          - splunk_version: "9.4.4"
+            splunk_filename: "splunk-9.4.4-f627d88b766b-linux-amd64.tgz"
         include:
           - kafka_version: "3.5.1"
             kafka_package: "kafka_2.12-3.5.1.tgz"
@@ -150,8 +155,8 @@ jobs:
             confluent_major_version: "7.9"
             confluent_package_version: "7.9.2"
     env:
-      CI_SPLUNK_VERSION: "10.0.0"
-      CI_SPLUNK_FILENAME: splunk-10.0.0-e8eb0c4654f8-linux-amd64.tgz
+      CI_SPLUNK_VERSION: ${{splunk_version}}
+      CI_SPLUNK_FILENAME: ${{splunk_filename}}
       CI_SPLUNK_HOST: 127.0.0.1
       CI_SPLUNK_PORT: 8089
       CI_SPLUNK_USERNAME: admin