Bump node from 18-alpine3.18 to 20-alpine3.18 in /clowarden-server

Bumps node from 18-alpine3.18 to 20-alpine3.18.

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

clowarden-server/Dockerfile

@@ -10,7 +10,7 @@ WORKDIR /clowarden/clowarden-server
 RUN cargo build --release
 
 # Build frontend
-FROM node:18-alpine3.18 AS frontend-builder
+FROM node:20-alpine3.18 AS frontend-builder
 RUN apk --no-cache add git
 WORKDIR /web
 COPY web .