CI: try to drive pixi workflow differently

Author: tacaswell

.github/workflows/smoke_test.yml

@@ -38,7 +38,7 @@ jobs:
       # set up pixi
       - uses: prefix-dev/[email protected]
         with:
-          environments: ['py310', 'py311', 'py312', 'py313']
+          environments: ${{ matrix.env }}
           pixi-version: v0.39.5
 
       # run install to see if it works