Enable Python 3.8 and 3.9 on M1 runners

These were excluded in 9ad28c3 (gitpython-developers#1817) due to
actions/setup-python#808, which was later
fixed by actions/python-versions#259.

Because Python 3.7 has been end-of-life for a while, it is very
unlikely to have AArch64 builds added in python-versions for use
on GitHub Actions CI runners (preinstalled or via setup-python).

.github/workflows/pythonpackage.yml

@@ -18,10 +18,6 @@ jobs:
         exclude:
         - os: "macos-14"
           python-version: "3.7"
-        - os: "macos-14"
-          python-version: "3.8"
-        - os: "macos-14"
-          python-version: "3.9"
         include:
         - experimental: false