drop support for Python <3.9, run tests for 3.13 (#300)

Author: finswimmer

.github/workflows/main.yml

@@ -17,7 +17,7 @@ jobs:
     strategy:
       matrix:
         os: [Ubuntu, macOS, Windows]
-        python-version: ["3.8", "3.9", "3.10", "3.11", "3.12"]
+        python-version: ["3.9", "3.10", "3.11", "3.12", "3.13"]
         include:
           - os: Ubuntu
             image: ubuntu-latest