CI: Use meson for openmp

Author: HaoZeke

.github/workflows/build.yml

@@ -36,11 +36,11 @@ jobs:
           channels: conda-forge,anaconda
       - name: Install dependencies
         run: |
-          conda install scipy numpy pytest 'setuptools<=60'
+          conda install scipy numpy pytest
       - name: Test
         run: |
-          python legacy_setup.py install --scs --openmp
-          pytest
+          python -m pip install -v . --no-build-isolation -Csetup-args=-Duse_openmp=true
+          pytest test
           rm -rf build/
 
   build_mkl: