Update GitHub Actions workflow for Python

Adds Python 3.13 to the test matrix and updates actions/checkout and actions/setup-python to their latest major versions for improved compatibility and security.

Author: Foxerine

.github/workflows/pythonapp.yml

@@ -13,11 +13,11 @@ jobs:
         runs-on: ubuntu-latest
         strategy:
             matrix:
-                python-version: [3.9]
+                python-version: [3.9, 3.13]
         steps:
-            - uses: actions/checkout@v2
+            - uses: actions/checkout@v4
             - name: Set up Python ${{ matrix.python-version }}
-              uses: actions/setup-python@v1
+              uses: actions/setup-python@v5
               with:
                   python-version: ${{ matrix.python-version }}
             - name: Display Python version