This is a work around for #6099
This is a backport of #6125
> Downgrade to macOS 10.15 as macOS 11.x breaks fuse2 testing.
>
> On macOS 10.15, osxfuse and also macfuse works with borg's fuse2 tests.
>
> Upgrading to macOS 11.x based github CI breaks the tests, see #6099,
> even when using the more recent macfuse to provide fuse2 capability.
> Why did you switch from osxfuse to macfuse?
> strictly taken, the switch was not required, it also worked with osxfuse after the macos downgrade.
>
> but considering a later potential upgrade of macos to some more recent version again (after the hanging issue is analyzed and fixed), i wanted to switch to the more recent macfuse code to be prepared for that.
