dependabot release_2.8-1.5 (SiliconLabsSoftware#189)

Author: Sarthak-Shaha

.github/dependabot.yml

@@ -13,4 +13,14 @@ updates:
     allow:
       - dependency-name: "third_party/matter_sdk"
       - dependency-name: "third_party/matter_support"
-    target-branch: "main"
+    target-branch: "main"
+
+  - package-ecosystem: "gitsubmodule"
+    directory: "/"
+    schedule:
+      interval: "daily"
+      time: "08:00"
+    allow:
+      - dependency-name: "third_party/matter_sdk"
+      - dependency-name: "third_party/matter_support"
+    target-branch: "release_2.8-1.5"