workflows: doc_build: fix addon name

Fixed a copy-pase error.
Replaced Matter with KNX IoT.

Signed-off-by: Adam Maciuga <adam.maciuga@nordicsemi.no>

Author: Adam-Maciuga

.github/workflows/doc_build.yml

@@ -143,7 +143,7 @@ jobs:
 
               if [ -n "${LINKS}" ]; then
                 echo ""
-                echo "Preview links for modified Matter add-on documents:"
+                echo "Preview links for modified KNX IoT add-on documents:"
                 echo ""
                 printf "%s" "${LINKS}"
               fi