explicitly mention the dest of toolchains argument

install-mpsd-software-environment.py

@@ -305,6 +305,7 @@ def main():
                     "--toolchain",  # allow singular as alternative 
                                     # (-> creates attribute `args.toolchains` if used)
                     type=str,
+                    dest="toolchains",
                     nargs="+",
                     default="NONE",
                     help="List of toolchains to install (use '--toolchains ALL' to install all toolchains). If nothing is specified, list of available toolchains for the release would be shown after creating the environment.",