os: return *PathError error in File.Sync on Plan 9

File.Sync was returning *SyscallError instead of *PathError on Plan 9.
Adjust the error type to match other systems.

Fixes #39800

Change-Id: I844e716eb61c193ef78d29cb0b4a3ef790bb3320
Reviewed-on: https://go-review.googlesource.com/c/go/+/239857
Reviewed-by: David du Colombier <[email protected]>

Author: fhs

src/os/file_plan9.go

@@ -233,10 +233,10 @@ func (f *File) Sync() error {
 	var buf [syscall.STATFIXLEN]byte
 	n, err := d.Marshal(buf[:])
 	if err != nil {
-		return NewSyscallError("fsync", err)
+		return &PathError{"sync", f.name, err}
 	}
 	if err = syscall.Fwstat(f.fd, buf[:n]); err != nil {
-		return NewSyscallError("fsync", err)
+		return &PathError{"sync", f.name, err}
 	}
 	return nil
 }