Supporting Stack on macOS/x86_64

[mpilgrem]

GitHub-hosted runners will cease to support macOS/x86_64 in about August 2027:

• [macOS] The additional macOS 15 Sonoma Intel-based image will be available in GitHub Actions actions/runner-images#13045

macOS Tahoe (macOS 26, released 15 September 2025) will be the last to support macOS/x86_64:

• https://arstechnica.com/gadgets/2025/06/apple-details-the-end-of-intel-mac-support-and-a-phaseout-for-rosetta-2/