chore(ci): hotfix github actions by using macos-12

[danceratopz]

🗒️ Description

Hotfix for the current issue we have in Github Actions (requires a proper follow-up fix!)

docs: freeze> python -m pip freeze --all
2 files would be left unchanged.
ERROR   -  "cairosvg" Python module is installed, but it crashed with:
no library called "cairo-2" was found
no library called "cairo" was found
no library called "libcairo-2" was found
cannot load library 'libcairo.so.2': dlopen(libcairo.so.2, 0x0002): tried: 'libcairo.so.2' (no such file), '/System/Volumes/Preboot/Cryptexes/OSlibcairo.so.2' (no such file), '/usr/lib/libcairo.so.2' (no such file, not in dyld cache), 'libcairo.so.2' (no such file), '/usr/local/lib/libcairo.so.2' (no such file), '/usr/lib/libcairo.so.2' (no such file, not in dyld cache).  Additionally, ctypes.util.find_library() did not manage to locate a library called 'libcairo.so.2'

Looks like a Github Actions update within the last 18 hours now points macos-latest to macos-14 (previously macos-12) which breaks tox -e docs.

🔗 Related Issues

None.

✅ Checklist

• All: Set appropriate labels for the changes.
• All: Considered squashing commits to improve commit history.
• All: Added an entry to CHANGELOG.md.
• All: Considered updating the online docs in the ./docs/ directory.
• Tests: All converted JSON/YML tests from ethereum/tests have been added to converted-ethereum-tests.txt.
• Tests: Included the type and version of evm t8n tool used to locally execute test cases: e.g., ref with commit hash or geth 1.13.1-stable-3f40e65.
• Tests: Ran mkdocs serve locally and verified the auto-generated docs for new tests in the Test Case Reference are correctly formatted.

[spencer-tb]

LGTM for a hotfix. Can have a look at this tomorrow in detail.