ci(macos): update Homebrew and smoke-test spell-check backend

[markiehill]

Fix the macOS spell-check regression (#2705) that persisted even after bundling only the applespell backend: on a clean machine the dictionary dropdown was still empty, regardless of the user's OS language.

Root cause: the macos-14 runner image pins a stale Homebrew snapshot with auto-update disabled, so brew install enchant poured enchant 2.8.16. Its AppleSpell provider uses a hard-wired language list that resolves to an empty dictionary set on current macOS. enchant 2.8.18 dropped the hard-wired list and reports the actual system dictionaries, so the shipped DMG needs enchant >= 2.8.18.

• Run brew update before installing so the fixed enchant bottle is used.
• Add a runtime smoke test: load the bundled libenchant exactly as the frozen app does (via PYENCHANT_LIBRARY_PATH) and assert it yields working dictionaries served by the bundled backend. A backend file can be present yet expose zero dictionaries, which the previous presence-only guard could not detect, so a broken backend now fails the build instead of shipping.

Summary:

Related Issue(s):

Reviewer's Checklist:

• The header of all files contain a reference to the repository license
• The overall test coverage is increased or remains the same as before
• All tests are passing
• All linting checks are passing and the style guide is followed
• Documentation (as docstrings) is complete and understandable
• Only files that have been actively changed are committed

[vkbo]

Thanks!

Could you trim down the massive blocks of AI-generated comments please? There's just too much of it.

[vkbo]

This branch also needs to be rebased onto release, otherwise it will not be included in the next release. Just switching base does not work since it is branched off of current main.