Fix testing matrix (#97)

* Add missing Python versions to test matrix

* Convert python-version entries to strings

When they are not strings, 3.10 is interpreted as 3.1 and causes CI to fail.

Author: ulgens

.github/workflows/ci.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [3.8, 3.12, 3.13]
+        python-version: ["3.8", "3.9", "3.10", "3.11", "3.12", "3.13"]
 
     steps:
     - uses: actions/checkout@v4