CI: Add Python 3.14 to test matrix

Add Python 3.14 to the test matrix of the main GitHub Actions workflow.

Author: EwoutH

.github/workflows/main.yml

@@ -44,7 +44,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
-        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"]
     env:
       GITHUB_PAT: ${{ secrets.GITHUB_TOKEN }}
     steps: