⬆️ Bump node from 20 to 21 in /docker

Bumps node from 20 to 21.

---
updated-dependencies:
- dependency-name: node
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

docker/Dockerfile

@@ -23,7 +23,7 @@ RUN flake8 . --exclude=migrations
 ################
 # NODE BUILDER #
 ################
-FROM node:20 as nodebuilder
+FROM node:21 as nodebuilder
 WORKDIR /app
 
 RUN npm install -g npm