dockerfiles/dut: use label instead of deprecated maintainer command

Fixes warnigns such as:

  WARN: MaintainerDeprecated: Maintainer instruction is deprecated in favor of using label

See also [1].

[1] https://docs.docker.com/reference/build-checks/maintainer-deprecated/

Signed-off-by: Bastian Krause <bst@pengutronix.de>
(cherry picked from commit 51df118)

Author: Bastian-Krause

dockerfiles/staging/dut/Dockerfile

@@ -1,6 +1,6 @@
 FROM debian:bookworm-slim
 
-MAINTAINER "Kasper Revsbech" <mail@krevsbech.dk>
+LABEL org.opencontainers.image.authors="mail@krevsbech.dk"
 
 ENV DEBIAN_FRONTEND=noninteractive