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>

remotes/docker/resolver_test.go

@@ -188,7 +188,7 @@ func TestBadTokenResolver(t *testing.T) {
 	if err == nil {
 		t.Fatal("Expected error getting token with inssufficient scope")
 	}
-	if errors.Cause(err) != ErrInvalidAuthorization {
+	if !errors.Is(err, ErrInvalidAuthorization) {
 		t.Fatal(err)
 	}
 }