Fix support for extras in micropip. ### Description

Fix for https://github.com/pyodide/pyodide/issues/2535

### Checklists

- [x] Add a [CHANGELOG](https://github.com/pyodide/pyodide/blob/main/docs/project/changelog.md) entry
- [x] Add / update tests

package:
  name: docutils
  version: 0.18.1
source:
  sha256: 23010f129180089fbcd3bc08cfefccb3b890b0050e1ca00c867036e9d161b98c
  url: https://files.pythonhosted.org/packages/8d/14/69b4bad34e3f250afe29a854da03acb6747711f3df06c359fa053fae4e76/docutils-0.18.1-py2.py3-none-any.whl
test:
  imports:
    - docutils

package:
  name: docutils
  version: 0.18.1
source:
  sha256: 23010f129180089fbcd3bc08cfefccb3b890b0050e1ca00c867036e9d161b98c
  url: https://files.pythonhosted.org/packages/8d/14/69b4bad34e3f250afe29a854da03acb6747711f3df06c359fa053fae4e76/docutils-0.18.1-py2.py3-none-any.whl
test:
  imports:
    - docutils
