Use try_insert to prevent panics

When using `insert` instead of `try_insert` on `EntityCommand`, it can
happen that the system panics, when the entity does not exist, even
when the `EntityCommand` has been accessed with `get_entity(...)`.
The following example demonstrates the problem:

```rust
if let Some(mut entity_commands) = commands.get_entity(entity) {
    // at this point some other system despawns `entity` concurrently
    entity_commands.insert(bundle);
    //              ^^^^^^ this will panic
}
```

This is also documented in the official bevy docs:
https://docs.rs/bevy/0.12.1/bevy/ecs/system/struct.Commands.html#method.get_entity

crates/bevy_picking_core/src/focus.rs

@@ -217,7 +217,7 @@ pub fn update_interactions(
         if let Ok(mut interaction) = interact.get_mut(hovered_entity) {
             *interaction = new_interaction;
         } else if let Some(mut entity_commands) = commands.get_entity(hovered_entity) {
-            entity_commands.insert(new_interaction);
+            entity_commands.try_insert(new_interaction);
         }
     }
 }