Fix release workflow: use macos-15-intel for x86_64 macOS builds

macos-13 runner was deprecated in December 2025. macos-15-intel is
the replacement for Intel macOS builds (available until August 2027).

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

Author: c

.github/workflows/release.yml

@@ -23,7 +23,7 @@ jobs:
             os: macos-latest
             use_cross: false
           - target: x86_64-apple-darwin
-            os: macos-13
+            os: macos-15-intel
             use_cross: false
 
     runs-on: ${{ matrix.os }}