ci: only build with 1 core to prevent swapping

Author: ahoarau

.github/workflows/ci-pixi.yml

@@ -50,7 +50,7 @@ jobs:
         run: pixi install
 
       - name: Configure & Build
-        run: pixi run build --verbose --parallel 2
+        run: pixi run build --verbose --parallel 1
 
       - name: Build documentation
         run: pixi run doc