CI: Use Python 3.13

Author: amotl

.github/workflows/main.yml

@@ -2,7 +2,7 @@
 name: Tests
 
 on:
-  pull_request: ~
+  pull_request:
   push:
     branches: [ main ]
 
@@ -23,7 +23,7 @@ jobs:
       fail-fast: false
       matrix:
         os: ["ubuntu-latest"]
-        python-version: ["3.9", "3.12"]
+        python-version: ["3.9", "3.13"]
 
     env:
       OS: ${{ matrix.os }}