Simplify fmt check in CI

Author: GuillaumeGomez

.github/workflows/ci.yml

@@ -103,10 +103,7 @@ jobs:
         ./y.sh test --release --clean --build-sysroot ${{ matrix.commands }}
 
     - name: Check formatting
-      run: |
-        cargo fmt -- --check
-        cd build_system
-        cargo fmt -- --check
+      run: ./y.sh fmt --check
 
     - name: clippy
       run: |