Fix output file permissions when using docker build. (#7378)

util/docker_build.sh

@@ -51,6 +51,7 @@ dir=$(pwd -W 2>/dev/null) || dir=$PWD  # Use Windows path if on Windows
 
 # Run container and build firmware
 docker run --rm -it $usb_args \
+	--user $(id -u):$(id -g) \
 	-w /qmk_firmware \
 	-v "$dir":/qmk_firmware \
 	-e ALT_GET_KEYBOARDS=true \