Allow macos on Python 3.8 to fail as GitHub CI has dropped support.

Closes jaraco/skeleton#124.

Author: jaraco

.github/workflows/main.yml

@@ -50,7 +50,7 @@ jobs:
         - python: pypy3.10
           platform: ubuntu-latest
     runs-on: ${{ matrix.platform }}
-    continue-on-error: ${{ matrix.python == '3.13' }}
+    continue-on-error: ${{ matrix.python == '3.13' || (matrix.python == '3.8' || matrix.python == '3.9') && matrix.platform == 'macos-latest' }}
     steps:
       - uses: actions/checkout@v4
       - name: Setup Python