Start testing on Python 3.13 with the CI (#153)

Author: bdraco

.codecov.yml

@@ -1,3 +1,3 @@
 codecov:
   notify:
-    after_n_builds: 10
+    after_n_builds: 13

.github/workflows/ci.yml

@@ -45,7 +45,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, windows-latest, macos-latest]
-        python-version: [ '3.9', '3.10', '3.11', '3.12' ]
+        python-version: [ '3.9', '3.10', '3.11', '3.12', '3.13' ]
         exclude:
           - os: macos-latest
             python-version: 3.9