copy: handle system security config issues with copy_file_range()

copy: handle system security config issues with copy_file_range()

* src/copy.c (sparse_copy): Upon EPERM from copy_file_range(),
fall back to a standard copy, which will give a more accurate
error as to whether the issue is with the source or destination.
Also this will avoid the issue where seccomp or apparmor are
not configured to handle copy_file_range(), in which case
the fall back standard copy would succeed without issue.
This specific issue with seccomp was noticed for example in:
https://github.com/golang/go/issues/40900