(ci) Upgrade to macos-13 CI runner image (#498)

macOS 11 support has been dropped in the GitHub-hosted CI runners:
actions/runner-images#9255. This has the
unpleasant effect of breaking all our CI until this gets merged.

Author: perlun

.github/workflows/perlang-install.yml

@@ -10,7 +10,7 @@ jobs:
         os:
           - ubuntu-20.04
           - ubuntu-22.04
-          - macos-11
+          - macos-13
 
     steps:
       - uses: actions/checkout@v1