ci: Use last pixi version

Author: jorisv

.github/workflows/macos-linux-windows-pixi.yml

@@ -70,7 +70,6 @@ jobs:
 
     - uses: prefix-dev/setup-pixi@v0.8.1
       with:
-        pixi-version: v0.31.0
         cache: true
         environments: ${{ matrix.environment }}