Bugfix: Fix directory sync errors related repositories accessed via SMB

On Linux and macOS accessing a repository via a SMB/CIFS mount resulted in
restic failing to save the lock file:

Save(<lock/071fe833f0>) returned error, retrying after 552.330144ms: sync /repo/locks: no such file or directory
Save(<lock/bf789d7343>) returned error, retrying after 552.330144ms: sync /repo/locks: invalid argument

This has been fixed by ignoring these error codes.

https://github.com/restic/restic/issues/3720
https://github.com/restic/restic/issues/3751
https://github.com/restic/restic/pull/3752
