fix lava emissive strength in depth of field example (#13449)

# Objective

- Since #13350 the lava is way too bright

![ba6ab328bc334085a237550e66ce91effa8950c7241ddef3eb10a8be336a68ef](https://github.com/bevyengine/bevy/assets/8672791/3a7aa7c0-5481-4616-8f84-2b69b57cf81c)

## Solution

- Change the emissive value in the material in the glb file from 20000
to 20

## Testing

- Run the example `depth_of_field`