Bump simulator to 21.4.0

Adopt lighty.io simulator version 21.4.0.

JIRA: LIGHTY-417
Signed-off-by: Ivan Hrasko <ivan.hrasko@pantheon.tech>

Author: ihrasko

.github/workflows/lighty-rnc-app/simulator/Dockerfile

@@ -1,4 +1,4 @@
-ARG SIMULATOR_VERSION="21.3.0"
+ARG SIMULATOR_VERSION="21.4.0"
 
 FROM alpine:3.23.3 AS clone