expand check to match Rails generated Dockerfiles

An example:
```
ARG RUBY_VERSION=3.4.2
FROM docker.io/library/ruby:$RUBY_VERSION-slim AS base
```

Author: rubys

lib/generators/dockerfile_generator.rb

@@ -418,7 +418,7 @@ def generate_app
       # Older versions no longer release new images
       matching_ruby = [">= 3.4.2", "~> 3.3.7", "~> 3.2.7", "~> 3.1.7"].any? { |v| Gem::Requirement.new(v).satisfied_by?(Gem.ruby_version) }
       # Only slim and alpine are missing libyaml-dev/yaml-dev
-      matching_image = /FROM ruby:.+-(alpine|slim)/i.match?(dockerfile)
+      matching_image = /FROM .*ruby:.+-(alpine|slim)/i.match?(dockerfile)
       if !matching_ruby || !matching_image
         missing.delete("libyaml-dev")
         missing.delete("yaml-dev")