Replace deprecated macos-13 runner with macos-15-intel

macos-13 was fully deprecated by GitHub Actions as of 2025-12-08
(actions/runner-images#13046), which is why that matrix leg hung in
queued indefinitely during testing. macos-15-intel is the replacement
label for x86_64 macOS builds, supported through August 2027.

Author: alexdma

.github/workflows/release.yml

@@ -27,7 +27,7 @@ jobs:
           - target: aarch64-unknown-linux-gnu
             os: ubuntu-24.04-arm
           - target: x86_64-apple-darwin
-            os: macos-13
+            os: macos-15-intel
           - target: aarch64-apple-darwin
             os: macos-14
           - target: x86_64-pc-windows-msvc