CI: add 3.13, remove 3.8

Author: dmerejkowsky

.github/workflows/tests.yml

@@ -13,7 +13,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.8", "3.9", "3.10", "3.11", "3.12"]
+        python-version: ["3.9", "3.10", "3.11", "3.12", "3.13"]
         os: [ubuntu-latest, macos-latest, windows-latest]
 
     steps: