Specify linux/amd64 as the docker build platform

The deb.nodesource.com archives only publish NodeJS packages for the
amd64 architecture.  Attempting to build this Dockerfile on a Apple
silicon Mac (aarch64 architecture) will result in an image that pulls
the incorrect version of `nodejs` from deb.debian.org instead.

Dockerfile

@@ -22,7 +22,7 @@
 # be world-readable!
 #
 #
-FROM debian:bullseye
+FROM --platform=linux/amd64 debian:bullseye
 
 #### Prepare the OS base setup ###