Error during upgrade to 10.1.1

[Ednt]

I run into the following error:

Current version is 10.0.12.
EspoCRM will be upgraded to version 10.1.1 now. Enter [Y] to continue.
Y
This may take a while. Do not close the terminal.
Downloading...
Upgrading...
Initialization...
Reverting...
Error: Permission denied:
vendor/guzzlehttp/guzzle/src/Handler/CurlFactory.php.bak

[Ednt]

Hm ...

a simple remove of this bak file solved the problem.
I don't know why this file was available.