ci: Migrate to macos-intel-15

Author: jorisv

.github/workflows/macos-linux-windows-pixi.yml

@@ -38,15 +38,15 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, macos-latest, macos-13]
+        os: [ubuntu-latest, macos-latest, macos-15-intel]
         environment: [all, all-py39]
         build_type: [Release, Debug]
         cxx_options: ['', '-mavx2']
 
         exclude:
           - os: macos-latest
             cxx_options: '-mavx2'
-          - os: macos-13
+          - os: macos-15-intel
             cxx_options: '-mavx2'
 
         include: