Disable Python 3.13 testing

Author: grossmj

.github/workflows/testing.yml

@@ -18,7 +18,7 @@ jobs:
     strategy:
       matrix:
         os: ["ubuntu-latest"]
-        python-version: ["3.8", "3.9", "3.10", "3.11", "3.12", "3.13"]
+        python-version: ["3.8", "3.9", "3.10", "3.11", "3.12"]
         #include:
           # only test with Python 3.10 on Windows
         #  - os: windows-latest