CI: Fix osx-x64 runner (macos-13 instead of macos-15-large)

Author: juanfranblanco

.github/workflows/build-shared-libs.yml

@@ -56,7 +56,7 @@ jobs:
           path: libbls_eth.dylib
 
   build-osx-x64:
-    runs-on: macos-15-large
+    runs-on: macos-13
     steps:
       - uses: actions/checkout@v4
       - name: Link shared library