message: fix custom loaders returning Arrays
diff: import { posix } from "../deps/path.ts";
  +import { isPlainObject } from "./utils.ts";
  import type { Data, Formats, Reader } from "../core.ts";
  @@ -85,7 +86,11 @@ export default class DataLoader {
  data[name] = fileData.content;
  } else {
  const target = data[name] as Record<string, unknown> | undefined;
  + if (isPlainObject(fileData) || target) {
  data[name] = Object.assign(target || {}, fileData);
  + } else {
  + data[name] = fileData;
  + }
  }
  return;
  