Test with multiple python versions.

Author: stefanseefeld

.github/workflows/test-ubuntu.yml

@@ -9,7 +9,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python: [python, python3]
+        python: [python, python3.9, python3.10, python3.11, python3.12, python3.13]
         cxx: [g++, clang++]
         std: [c++98, c++11, c++14, c++17]
         include: