update pixi

Author: glemaitre

.github/workflows/tests.yml

@@ -39,7 +39,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: prefix-dev/[email protected]
         with:
-          pixi-version: v0.31.0
+          pixi-version: v0.39.0
           environments: ${{ matrix.environment }}
           # we can freeze the environment and manually bump the dependencies to the
           # latest version time to time.