chore(deps): update python docker tag to v3.12

Author: renovate[bot]

Dockerfile

@@ -1,5 +1,5 @@
 # borrowing from https://www.digitalocean.com/community/tutorials/how-to-build-and-deploy-a-flask-application-using-docker-on-ubuntu-18-04
-FROM python:3.9
+FROM python:3.12
 #ENV STATIC_URL /static
 #ENV STATIC_PATH /var/www/app/static
 # will be overwritten by whatever volume we attach (for dev), but (I believe) in prod we have no volumne, so grab all the files at the start