[SL-TEMP] Point the matter_support submodule to release_2.6-1.4 (#318)

Author: selissia

.gitmodules

@@ -208,7 +208,7 @@
 [submodule "third_party/silabs/matter_support"]
 	path = third_party/silabs/matter_support
 	url = https://github.com/SiliconLabs/sdk_support.git
-	branch = main
+	branch = release_2.6-1.4
 	platforms = silabs,silabs_docker
 [submodule "third_party/silabs/simplicity_sdk"]
 	path = third_party/silabs/simplicity_sdk