Update devcontainer to use ruby version 3.4.2

- Ruby version installed with this commit:
```
vscode ➜ /workspaces/rails (ruby342_devcontainer) $ ruby -v
ruby 3.4.2 (2025-02-15 revision d2930f8e7a) +PRISM [aarch64-linux]
```

Ruby 3.4.2 is available at:
https://github.com/rails/devcontainer/pkgs/container/devcontainer%2Fimages%2Fruby/356224599?tag=3.4.2
rails/devcontainer@00a473a

Author: yahonda

.devcontainer/Dockerfile

@@ -1,7 +1,7 @@
 # See here for image contents: https://github.com/microsoft/vscode-dev-containers/tree/v0.191.1/containers/ruby/.devcontainer/base.Dockerfile
 
 # [Choice] Ruby version: 3.4, 3.3, 3.2
-ARG VARIANT="3.4.1"
+ARG VARIANT="3.4.2"
 FROM ghcr.io/rails/devcontainer/images/ruby:${VARIANT}
 
 RUN sudo apt-get update && export DEBIAN_FRONTEND=noninteractive \