[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

@@ -3,7 +3,7 @@
 # - .github/dependabot.yml (fjern versjonspin for docker)
 # - packages.json under "engines" (her leter dependabot npm)
 # - .ncurc.js (automatiske oppdateringer for node-types)
-FROM node:20-alpine AS dependencies
+FROM node:21-alpine AS dependencies
 
 WORKDIR /app
 COPY package.json .
@@ -13,7 +13,7 @@ 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:20-alpine AS builder
+FROM node:21-alpine AS builder
 
 ARG DIGISOS_ENV
 ENV NEXT_PUBLIC_DIGISOS_ENV=${DIGISOS_ENV}
@@ -26,7 +26,7 @@ RUN npm run build
 RUN npm prune --production
 
 
-FROM node:20-slim AS release
+FROM node:21-slim AS release
 
 ARG DIGISOS_ENV