Fix macOS ARM64(m1) GHA issues

[kesara]

Describe the issue

macos-latest GitHub runners run on arm64 (m1) architecture.
These runners fail to run tests with errors:

Traceback (most recent call last):
  File "/Users/runner/work/xml2rfc/xml2rfc/test.py", line 8, in <module>
    import xml2rfc

  File "/Users/runner/work/xml2rfc/xml2rfc/xml2rfc/__init__.py", line 38, in <module>
-----

    from weasyprint.text.ffi import pango
WeasyPrint could not import some external libraries. Please carefully follow the installation steps before reporting an issue:
  File "<frozen importlib._bootstrap>", line 1360, in _find_and_load
https://doc.courtbouillon.org/weasyprint/stable/first_steps.html#installation
  File "<frozen importlib._bootstrap>", line 1322, in _find_and_load_unlocked
https://doc.courtbouillon.org/weasyprint/stable/first_steps.html#troubleshooting 
  File "<frozen importlib._bootstrap>", line 1262, in _find_spec

  File "<frozen importlib._bootstrap_external>", line 1528, in find_spec
-----
  File "<frozen importlib._bootstrap_external>", line 1497, in _get_spec

  File "<frozen importlib._bootstrap_external>", line 1368, in __iter__

  File "<frozen importlib._bootstrap_external>", line 1355, in _recalculate
-----
  File "<frozen importlib._bootstrap_external>", line 1351, in _get_parent_path

KeyError: 'weasyprint'
WeasyPrint could not import some external libraries. Please carefully follow the installation steps before reporting an issue:
https://doc.courtbouillon.org/weasyprint/stable/first_steps.html#installation
https://doc.courtbouillon.org/weasyprint/stable/first_steps.html#troubleshooting 

See https://github.com/ietf-tools/xml2rfc/actions/runs/9511526289/job/26217825833?pr=1124

A quick fix for this is to restrict to macos-12 so the tests will run on intel architecture.

The issue seems to be GitHub-related since I can't reproduce these errors locally on macOS 14.5 with arm64 (m1).

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