[docker]: Bump node from 20-slim to 21-slim

Bumps node from 20-slim to 21-slim.

---
updated-dependencies:
- dependency-name: node
  dependency-type: direct:production
...

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

Dockerfile

@@ -4,7 +4,7 @@
 # - packages.json under "engines" (her leter dependabot npm)
 # - .ncurc.js (automatiske oppdateringer for node-types)
 # pt er vi på node 18 fordi ellers plager dekoratoren oss med "body has already been consumed"
-FROM node:18-alpine AS dependencies
+FROM node:21-alpine AS dependencies
 
 WORKDIR /app
 COPY package.json .
@@ -14,7 +14,7 @@ COPY .npmrc.dockerbuild .npmrc
 RUN --mount=type=secret,id=NODE_AUTH_TOKEN NODE_AUTH_TOKEN=$(cat /run/secrets/NODE_AUTH_TOKEN) \
     npm ci --prefer-offline --no-audit
 
-FROM node:18-alpine AS builder
+FROM node:21-alpine AS builder
 
 ARG DIGISOS_ENV
 ARG LOGIN_SESSION_API_URL