dockerfile: pin node version

node:22 has been released yesterday and it is broken. With node 22,
after `npm install`, the directory ./node_modules/.bin is empty, and you
should call `npm install` twice.

Instead, pinning to a working version of the node image works.

Dockerfile

@@ -1,10 +1,11 @@
 #
 # Javascript builder for static files
 #
-FROM node AS node-builder
+FROM node:20 AS node-builder
 
 WORKDIR /app
 COPY package.json package-lock.json /app/
+
 RUN npm install
 
 #
@@ -88,4 +89,4 @@ CMD python manage.py makemigrations && python manage.py migrate && \
   --limit-post=24000000 \
   --http-manage-expect \
   --ignore-sigpipe --ignore-write-errors --disable-write-exception \
-  --cron='0 -1 -1 -1 -1 poetry run python /app/manage.py runcrons'
+  --cron='0 -1 -1 -1 -1 poetry run python /app/manage.py runcrons'