Update git_refs.go (#1240)

Author: dprotaso

github/git_refs.go

@@ -69,7 +69,7 @@ func (s *GitService) GetRef(ctx context.Context, owner string, repo string, ref
 	if _, ok := err.(*json.UnmarshalTypeError); ok {
 		// Multiple refs, means there wasn't an exact match.
 		return nil, resp, errors.New("multiple matches found for this ref")
-	} else if resp.StatusCode == 404 {
+	} else if _, ok := err.(*ErrorResponse); ok && resp.StatusCode == 404 {
 		// No ref, there was no match for the ref
 		return nil, resp, errors.New("no match found for this ref")
 	} else if err != nil {