Rendering two 3d passes to the same window only shows the last pass when MSAA is enabled

## Bevy version

https://github.com/HackerFoo/bevy/tree/two_passes_main

## Operating system & version

MacOS 12.1

## What you did

This will show a red and a green cube spinning:

    cargo run --example two_passes

Setting the MSAA samples to 4 will only show one cube.