Feedback "Moving file failed" during import, improve handling of this case

I upgraded Unity to 2020.1.0b11 and opened the project from Case 1108597. While opening the project, I was presented with several of these dialogs (always a different file). It was the first time that this occurred during an project upgrade ever for me.



Just clicking "Try Again" made it work.

My suggestion:
In order to reduce these "false positives", if Unity can't move a file, wait a few milliseconds and try again automatically. In most cases, it will probably succeed then. If it doesn't succeed the 2nd or 3rd try, display the error.

I run into this problem usually during a build:


This issue is not bound to my PC, I've observed this on my work PC too (don't have access to it atm though).