Update screenshot format examples in config

In the screenshot configuration of the utility settings, the example values for the screenshot format are updated to simple file extensions 'jpg', 'png', and 'webp', instead of the MIME types.

src/Resources/config/definition/utils/screenshots.php

@@ -49,7 +49,7 @@ function getScreenshotsNode(string $info): ArrayNodeDefinition
         ->end()
         ->scalarNode('format')
         ->info('The format of the screenshot. Will convert the file if set.')
-        ->example(['image/jpg', 'image/png', 'image/webp'])
+        ->example(['jpg', 'png', 'webp'])
         ->end()
         ->scalarNode('reference')
             ->defaultNull()