Bump node from 21.5-alpine to 21.6-alpine

Bumps node from 21.5-alpine to 21.6-alpine.

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

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

Dockerfile

@@ -1,4 +1,4 @@
-FROM node:21.5-alpine as node
+FROM node:21.6-alpine as node
 COPY . /shlink-web-client
 ARG VERSION="latest"
 ENV VERSION ${VERSION}