ci: use the versioned Debian WSL identifier

setup-wsl v7 removes the deprecated unversioned Debian distribution, causing every Windows matrix job to stop during environment setup. Select Debian-11, the documented replacement for the old Debian identifier, to preserve the workflow environment while allowing the action upgrade.

Author: codex

.github/workflows/pythonpackage.yml

@@ -69,7 +69,7 @@ jobs:
       uses: Vampire/setup-wsl@v7.0.0
       with:
         wsl-version: 1
-        distribution: Debian
+        distribution: Debian-11
 
     - name: Prepare this repo for tests
       run: |