Replace unknown attribute norun with no_run, as per the warning

Author: linkmauve

renderer/src/concurrent/executor.rs

@@ -14,7 +14,7 @@
 pub trait Executor {
     /// Like the Rayon snippet:
     ///
-    /// ```norun
+    /// ```no_run
     /// (0..length).into_par_iter().map(builder).collect()
     /// ```
     fn build_vector<T, F>(&self, length: usize, builder: F) -> Vec<T>

renderer/src/concurrent/scene_proxy.rs

@@ -92,7 +92,7 @@ impl SceneProxy {
     ///
     /// Exactly equivalent to:
     ///
-    /// ```norun
+    /// ```no_run
     /// scene_proxy.build(build_options);
     /// scene_proxy.render(renderer);
     /// }