ci: update GitHub Actions using deprecated Node.js 20

[davidpoblador]

Problem

GitHub warns that two actions in release.yml and test-ghostty.yml use Node.js 20, which will be forced to Node.js 24 by June 2, 2026:

• mlugg/setup-zig@v2
• xavierLowmiller/xcodegen-action@1.2.4

Node.js 20 actions are deprecated. Actions will be forced to run with Node.js 24
by default starting June 2nd, 2026.

Fix

Check for newer versions of these actions that support Node.js 24:

• setup-zig: check https://github.com/mlugg/setup-zig for a v3 or updated v2
• xcodegen-action: check https://github.com/xavierLowmiller/xcodegen-action for updates. Alternatively, replace with a simple brew install xcodegen or direct download step we control.

Affected workflows

• .github/workflows/release.yml
• .github/workflows/test-ghostty.yml

Reference

Build: https://github.com/alltuner/factoryfloor/actions/runs/23294661860/job/67738861416