Custom thumbnails don't get updated until the asset is saved

This is a regression, here's the repro in FN/Main (48954958) : [Link Removed]

^{And now in UE5.7 (48496583) : [Link Removed]}

Steps to Reproduce:

1. Open any project in Unreal Editor
2. Open any level
3. Right-click on any asset in the content browser to set a custom thumbnail: Common menu subsection: Asset Actions -> Capture Thumbnail
4. Observe the thumbnails for the asset in the Content Browser 

Actual Result: The default thumbnail is displayed in the Content Browser 

Expected result: The captured area from the viewport is set as the thumbnail for the asset in the Content Browser