add setup-python to 3.13

dependabot wants to bump jsonschema to 4.26.0, which is incompatible with the older python that defaults on windows-2022 (or windows-default).

research indicates that the best solution is to always use setup-python action to get reasonably-recent python in the action.

Author: pryrt

.github/workflows/CI_build.yml

@@ -16,6 +16,11 @@ jobs:
     - name: Checkout repo
       uses: actions/checkout@v6
 
+    - name: Set up Python 3.13
+      uses: actions/setup-python@v6
+      with:
+        python-version: '3.13' # Uses the latest patch version of the given version
+
     - name: Install python modules
       working-directory: .
       run: python -m pip install -r requirements.txt