Bump node in /docker/backend

Bumps node from 20.13.1-buster-slim to 20.14.0-buster-slim.

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

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

docker/backend/Dockerfile

@@ -1,4 +1,4 @@
-FROM node:20.13.1-buster-slim AS builder
+FROM node:20.14.0-buster-slim AS builder
 
 ARG commitHash
 ENV MEMPOOL_COMMIT_HASH=${commitHash}
@@ -24,7 +24,7 @@ RUN npm install --omit=dev --omit=optional
 WORKDIR /build
 RUN npm run package
 
-FROM node:20.13.1-buster-slim
+FROM node:20.14.0-buster-slim
 
 WORKDIR /backend