ci(release): swap retired macos-13 runner for macos-15-intel (#292)

The macos-13 GitHub-hosted image was deprecated 2025-09-22 and **fully
unsupported from 2025-12-04** (actions/runner-images#13046, #13402,
#13634). Any matrix entry pinning `os: macos-13` now queues forever
against a runner that does not exist — observed on the v0.1.0 release
run (26124042846): linux-x64 + macos-arm64 finished in minutes; the
macos-x64 leg sat queued ~10 h before I cancelled it. The
`checksums` job (`needs: build`) never ran, so no SHA256SUMS landed
on the Release, leaving INT-10 (#282) stuck.

`macos-15-intel` is the current Intel macOS x64 standard runner
(per actions/runner-images README, alongside `macos-15-large`,
`macos-latest-large`, `macos-26-intel`). macOS 15 is the safer of the
two: stable GA image, in contrast to macos-26 which only graduated
out of public beta in 2026-02 and had an arm-label regression as
recently as actions/runner-images#14112 (closed 2026-05-19).

No other change. Target name (`macos-x64`) and asset-name contract
(`affinescript-macos-x64`, ADR-019) are unchanged — only the build
host is swapped. Effect: the next `v*` tag push (or a `workflow_dispatch`
escape hatch if added later) will produce the missing macos-x64 binary
+ a complete SHA256SUMS, which the follow-up shim release can pin.

Refs #282, #260. Unblocks #291.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

.github/workflows/release.yml

@@ -52,7 +52,7 @@ jobs:
         include:
           - os: ubuntu-latest
             target: linux-x64
-          - os: macos-13
+          - os: macos-15-intel
             target: macos-x64
           - os: macos-14
             target: macos-arm64