ci: use no Debian WSL identifier (as default is new enough)

setup-wsl v7 removes the deprecated unversioned Debian distribution, causing
every Windows matrix job to stop during environment setup. Select Debian-13 implicitly,
the documented replacement for the old Debian identifier, to preserve the workflow
environment while allowing the action upgrade.

Co-authored-by: Eliah Kagan <degeneracypressure@gmail.com>

Author: Byron

.github/workflows/pythonpackage.yml

@@ -69,7 +69,6 @@ jobs:
       uses: Vampire/setup-wsl@v7.0.0
       with:
         wsl-version: 1
-        distribution: Debian
 
     - name: Prepare this repo for tests
       run: |