ci: pin python version 3.13 within regression test

Author: harryswift01

.github/workflows/pr.yaml

@@ -88,7 +88,7 @@ jobs:
       - name: Set up Python 3.14
         uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405
         with:
-          python-version: "3.14"
+          python-version: "3.13"
           cache: pip
 
       - name: Install testing dependencies