Replace errors.Cause() with errors.Is()

Dependencies may be switching to use the new `%w` formatting
option to wrap errors; switching to use `errors.Is()` makes
sure that we are still able to unwrap the error and detect the
underlying cause.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

unpacker.go

@@ -265,7 +265,7 @@ func (u *unpacker) fetch(ctx context.Context, h images.Handler, layers []ocispec
 			if u.limiter != nil {
 				u.limiter.Release(1)
 			}
-			if err != nil && errors.Cause(err) != images.ErrSkipDesc {
+			if err != nil && !errors.Is(err, images.ErrSkipDesc) {
 				return err
 			}
 			close(done[i])