DEV: Don't run dev-only code in specs (discourse#23427)

This was causing the following notice to be printed out when running system specs:

```
I did no detect a custom `config/dev.yml` file, creating one for you where you can amend defaults.
```

(since 61571be)

lib/discourse_dev/config.rb

@@ -16,7 +16,7 @@ def initialize
       if File.exist?(file_path)
         user_config = YAML.load_file(file_path, permitted_classes: [Date])
       else
-        puts "I did no detect a custom `config/dev.yml` file, creating one for you where you can amend defaults."
+        puts "Did not detect `config/dev.yml`, creating one for you where you can amend defaults."
         FileUtils.cp(default_file_path, file_path)
         user_config = {}
       end

lib/faker/discourse_markdown.rb

@@ -86,7 +86,7 @@ def load_image(image)
 
       def available_methods
         methods = super
-        methods << :image if ::DiscourseDev.config.post[:include_images]
+        methods << :image if Rails.env.dev? && ::DiscourseDev.config.post[:include_images]
         methods
       end
     end