Use loky.cpu_count() instead of os.cpu_count(). <!-- Thank you for contributing to Pyodide! All improvements are welcome,
     so don't be afraid to make a PR. -->

### Description

As discussed in https://github.com/pyodide/pyodide/pull/3559#issuecomment-1435965170

### Checklists

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

package:
  name: mne
  version: 1.2.3
  top-level:
    - mne
source:
  sha256: 0a722244eac3eb9ff5c5c45576491cbad7741a69d38e05478303842ee7c3daac
  url: https://files.pythonhosted.org/packages/eb/66/0b755f8b0520706942731d28c70e45d97f87a5193c8053439c2ebbebd0fb/mne-1.2.3-py3-none-any.whl
requirements:
  run:
    - distutils
    - numpy
    - scipy
    - setuptools
    - decorator
about:
  home: https://mne.tools/dev/
  PyPI: https://pypi.org/project/mne
  summary: MNE-Python project for MEG and EEG data analysis.
  license: BSD-3-Clause

package:
  name: mne
  version: 1.2.3
  top-level:
    - mne
source:
  sha256: 0a722244eac3eb9ff5c5c45576491cbad7741a69d38e05478303842ee7c3daac
  url: https://files.pythonhosted.org/packages/eb/66/0b755f8b0520706942731d28c70e45d97f87a5193c8053439c2ebbebd0fb/mne-1.2.3-py3-none-any.whl
requirements:
  run:
    - distutils
    - numpy
    - scipy
    - setuptools
    - decorator
about:
  home: https://mne.tools/dev/
  PyPI: https://pypi.org/project/mne
  summary: MNE-Python project for MEG and EEG data analysis.
  license: BSD-3-Clause
