Use macos-13 (Intel) runner for x86_64 desktop build

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: mikkeldamsgaard

.github/workflows/release.yml

@@ -75,7 +75,7 @@ jobs:
           - os: macos-latest
             target: aarch64-apple-darwin
             artifact: ralph-desktop-macos-arm64
-          - os: macos-latest
+          - os: macos-13
             target: x86_64-apple-darwin
             artifact: ralph-desktop-macos-x86_64
           - os: windows-latest