Run long Lean builds on macOS runners

Author: mfornet

.github/workflows/lean_action_ci.yml

@@ -9,7 +9,7 @@ on:
 jobs:
   codelib:
     name: Build CodeLib proofs
-    runs-on: ubuntu-latest
+    runs-on: macos-latest
     steps:
       - uses: actions/checkout@v4
       - uses: actions/cache@v4
@@ -26,7 +26,7 @@ jobs:
 
   programs:
     name: Build program proofs
-    runs-on: ubuntu-latest
+    runs-on: macos-latest
     steps:
       - uses: actions/checkout@v4
       - uses: actions/cache@v4