.github/workflows/dist.yml: Replace macos-13 runner by macos-15-intel

Author: mkoeppe

.github/workflows/dist.yml

@@ -50,7 +50,7 @@ jobs:
             arch: i686
           - os: ubuntu-24.04-arm
             arch: aarch64
-          - os: macos-13
+          - os: macos-15-intel
             arch: x86_64
           - os: macos-14
             arch: arm64