manually install ninja in ci

.github/workflows/ci-sage.yml → .github/workflows/ci.yml

@@ -104,6 +104,7 @@ jobs:
       run: |
           pip install --upgrade pip
           pip install --upgrade -r requirements.txt
+          pip install --upgrade ninja
     - name: Build
       run: pip install --no-build-isolation --config-settings=builddir=builddir .
     - name: Test