dependabot-docker(deps): bump node from 14 to 21 in /.devcontainer

Bumps node from 14 to 21.

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

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

.devcontainer/Dockerfile

@@ -1,5 +1,5 @@
 # Use an official Node runtime as a parent image
-FROM node:14
+FROM node:21
 
 # Set the working directory
 WORKDIR /usr/src/app