maint: add Python 3.14 to supported version

Author: DimitriPapadopoulos

.github/workflows/pythonpackage.yml

@@ -23,7 +23,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ['3.9', '3.10', '3.11', '3.12', '3.13']
+        python-version: ['3.9', '3.10', '3.11', '3.12', '3.13', '3.14']
 
     steps:
     - uses: actions/checkout@v4
@@ -33,6 +33,7 @@ jobs:
       uses: actions/setup-python@v5
       with:
         python-version: ${{ matrix.python-version }}
+        allow-prereleases: true
     - name: Build and check package
       run: |
         pipx run build