add 3.12 bc upstream has it

Author: sneakers-the-rat

.github/workflows/test-upstream.yaml

@@ -10,7 +10,7 @@ jobs:
     strategy:
       matrix:
         os: [ ubuntu-latest, windows-latest ]
-        python-version: [ "3.8", "3.9", "3.10", "3.11" ]
+        python-version: [ "3.8", "3.9", "3.10", "3.11", "3.12" ]
         exclude:
           - os: windows-latest
             python-version: "3.8"