Update testing.yml (#356)

Remove working around for macOs latest.
Issue since fixed:
actions/setup-python#696 (comment)

Author: gcattan

.github/workflows/testing.yml

@@ -18,12 +18,6 @@ jobs:
       matrix:
         python-version: [3.9, "3.10", 3.11]
         os: [ubuntu-latest, macOS-latest, windows-latest]
-        # Python 3.9 is on macos-13 but not macos-latest (macos-14-arm64)
-        # https://github.com/actions/setup-python/issues/696#issuecomment-1637587760
-        exclude:
-        - { python-version: "3.9", os: "macos-latest" }
-        include:
-        - { python-version: "3.9", os: "macos-13" }
 
     steps:
     - uses: actions/checkout@v4