workflows: Fix duplicate 3.11 job

This fixes the following two problems:

- GitHub Actions generated two separate jobs for Python 3.11
  because the "python-version" and "experimental" lists in the
  CI matrix generated a job for it with experimental=false, and
  then the "include" list that augments the CI matrix generated a
  separate job for it with experimental=true.

- The list of jobs is somewhat difficult to understand in the
  GitHub Actions interface, because the "python-version" and
  "experimental" keys are show in different orders, due to the
  different orders the workflow file listed them.

.github/workflows/pythonpackage.yml

@@ -37,8 +37,8 @@ jobs:
  strategy:
  fail-fast: true
  matrix:
+ python-version: ["3.7", "3.8", "3.9", "3.10"]
  experimental: [false]
- python-version: ["3.7", "3.8", "3.9", "3.10", "3.11"]
  include:
  - python-version: "3.11"
  experimental: true