Update to Node 22 (active LTS)

- See https://nodejs.org/en/blog/release/v22.11.0
- See https://github.com/wagtail/wagtail/issues/12531

Dockerfile.frontend

@@ -1,4 +1,4 @@
-FROM node:20-slim
+FROM node:22-slim
 LABEL maintainer="hello@wagtail.org"
 
 RUN apt-get update && apt-get install rsync make -y