fix: add new Splunk version 9.4.0 (#183)

Splunk 9.4 was released and image published on Dockerhub on 31.12.2024
CI is broken as of now so creating this PR manually.

Test runs:
-
https://github.com/splunk/splunk-add-on-for-google-workspace/actions/runs/12653931014
-
https://github.com/splunk/splunk-add-on-for-cisco-meraki/actions/runs/12653924089

action.yml

@@ -3,4 +3,4 @@ name: "Add on factory test matrix"
 description: "This tool automates the selection matrix dimensions"
 runs:
   using: "docker"
-  image: docker://ghcr.io/splunk/addonfactory-test-matrix-action/addonfactory-test-matrix-action:v2.1.11
+  image: Dockerfile

config/splunk_matrix.conf

@@ -1,7 +1,17 @@
 [GENERAL]
-LATEST = 9.3
+LATEST = 9.4
 OLDEST = 9.1
 
+[9.4]
+VERSION = 9.4.0
+BUILD = 6b4ebe426ca6
+SUPPORTED = 2026-12-16
+PYTHON3 = true
+PYTHON2 = false
+SWC = true
+METRICS_MULTI = true
+INPUT_LOOKUP = true
+
 [9.3]
 VERSION = 9.3.2
 BUILD = d8bb32809498