example showcase: switch default api to webgpu (#9193)

# Objective

- in #9168 I did some change to the showcase script, introducing the
notion of web api and setting the default Web API to webgl2
- that script was actually only called for webgpu example, so that
should have been the default value

tools/example-showcase/src/main.rs

@@ -53,7 +53,7 @@ enum Action {
  /// Path to the folder where the content should be created
  content_folder: String,
 
- #[arg(value_enum, long, default_value_t = WebApi::Webgl2)]
+ #[arg(value_enum, long, default_value_t = WebApi::Webgpu)]
  /// Which API to use for rendering
  api: WebApi,
  },