ci: use python 3.8 for builds

this should allow for windows 7 support

.github/workflows/build.yaml

@@ -14,7 +14,7 @@ jobs:
     - uses: actions/checkout@v4
     - uses: actions/setup-python@v5
       with:
-        python-version: '3.9'
+        python-version: '3.8'
 
     - name: Install pyinstaller and dependencies
       run: pip3 install --upgrade pyinstaller -r requirements.txt