Update python version in Makefile as well

Author: mathbunnyru

Makefile

@@ -38,7 +38,7 @@ help:
 # Note that `ROOT_IMAGE` and `PYTHON_VERSION` arguments are only applicable to `docker-stacks-foundation` image
 build/%: DOCKER_BUILD_ARGS?=
 build/%: ROOT_IMAGE?=ubuntu:24.04
-build/%: PYTHON_VERSION?=3.12
+build/%: PYTHON_VERSION?=3.13
 build/%: ## build the latest image for a stack using the system's architecture
 	docker build $(DOCKER_BUILD_ARGS) --rm --force-rm \
 	  --tag "$(REGISTRY)/$(OWNER)/$(notdir $@):latest" \