Update ruby Docker tag to v4 (#38)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [ruby](https://hub.docker.com/_/ruby)
([source](https://redirect.github.com/docker-library/ruby)) | final |
major | `3.4-slim-bookworm` → `4.0-slim-bookworm` |

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rails-dev/Dockerfile

@@ -1,4 +1,4 @@
-FROM ruby:3.4-slim-bookworm@sha256:514336e7d46dd52b94a7391e4bc34dc04dc83098963c2c2493b90354952acd78
+FROM ruby:4.0-slim-bookworm@sha256:c5650da02325ecb3e7dd96e7074772c3ae2ecd093a9acf2cdbcf1a2fdc680726
 
 # Install essential packages
 RUN apt-get update && apt-get install -y \