Avoid errors on Python 3.8 macos-latest as GitHub CI has dropped support

Author: abravalheri

.github/workflows/main.yml

@@ -61,6 +61,12 @@ jobs:
         - platform: ubuntu-latest
           python: "3.10"
           distutils: stdlib
+        # Python 3.9 is on macos-13 but not macos-latest (macos-14-arm64)
+        # https://github.com/actions/setup-python/issues/850
+        # https://github.com/actions/setup-python/issues/696#issuecomment-1637587760
+        - {python: "3.8", platform: "macos-13"}
+        exclude:
+        - {python: "3.8", platform: "macos-latest"}
     runs-on: ${{ matrix.platform }}
     continue-on-error: ${{ matrix.python == '3.13' }}
     env: