Don't fail for too many retries before intended

Minor bug introduced by updated logic, could have resulted in a successful copy
that got rejected because it retried one too many times.

Copy-Robust.ps1

···
             }
         }
 
-        if ( $count -ge 3 ) {
+        if ( $count -ge 4 ) {
             Write-Error "Failed to copy `"$local_path`" after 3 retries, aborting"
             return
         }