add CI run using python 3.13

Author: murrayrm

.github/workflows/python-package-conda.yml

@@ -22,7 +22,7 @@ jobs:
         cvxopt: ["", "conda"]
         mplbackend: [""]
         include:
-          - python-version: '3.12'
+          - python-version: '3.13'
             slycot: conda
             pandas: conda
             cvxopt: conda