message: Update writing-custom-field-extensions.md
  refactored the import
diff: @@ -81,8 +81,7 @@ import {
  scaffolderPlugin,
  createScaffolderFieldExtension,
  } from '@backstage/plugin-scaffolder';
  -import { MyCustomExtension } from './MyCustomExtension';
  -import { myCustomValidation } from './MyCustomExtension';
  +import { MyCustomExtension, myCustomValidation } from './MyCustomExtension';
  export const MyCustomFieldExtension = scaffolderPlugin.provide(
  createScaffolderFieldExtension({
  