dynamic_types.rs example panics when run due to failed assert

Originally noticed by @ChristopherBiscardi in https://github.com/bevyengine/bevy/pull/24748#discussion_r3570195791_

The assert in question: https://github.com/bevyengine/bevy/blob/6d4f6979cf018ab84c7f630b7192577c62afdda5/examples/reflection/dynamic_types.rs#L103

This is actually a regression from #21137 by @SkiFire13 (<3), not the fault of #24748 and is broken on main: the pattern documented as broken in that example now works, and so asserting that it's none is incorrect!

## Solution

We should update this example, and the doc test for TypedReflectDeserializer, to match the actual implemented logic.

Start with examples/reflection/dynamic_types.rs at the assert linked in the issue, then find the TypedReflectDeserializer doc test. Run the example and relevant doc test to reproduce the panic; done means both match the implemented logic and pass without asserting the now-working pattern is None.

Written by the indexing model from the issue text.