Document name area does not update with template part name

[noahtallen]

Describe the bug
In the site editor, it is possible to "zoom in" to an individual template part. However, the document name does not update in this case. As you can see in the screenshot, the document title is still the template name:

To reproduce
Steps to reproduce the behavior:

1. Set up a block-based theme and the FSE experiment in gutenberg
2. Go to the site editor
3. Select a template part from the nav sidebar
4. See issue

Expected behavior
It should display the template part name if we have zoomed into a template part.