fix yaml

Author: rflamary

.github/workflows/build_tests.yml

@@ -245,12 +245,11 @@ jobs:
   #       python -m pytest --durations=20 -v test/ ot/ --color=yes --cov=./ --cov-report=xml
 
   macos:
-     runs-on: ${{ matrix.os }}
+     runs-on: macos-latest
      if: "!contains(github.event.head_commit.message, 'no ci')"
      strategy:
        max-parallel: 4
        matrix:
-         os: [macos-latest]
          python-version: [${{ env.PY_VERSION }},]
 
      steps: