remove OS conditional

Author: ngoldbaum

.github/workflows/ci.yaml

@@ -429,15 +429,9 @@ jobs:
         python -m pip install .
 
     - name: run tests under pytest-run-parallel
-      if: runner.os == 'Windows'
       run: |
         python -m pytest --parallel-threads=4 --skip-thread-unsafe=True
 
-    - name: run tests under pytest-run-parallel
-      if: runner.os != 'Windows'
-      run: |
-        python -m pytest --parallel-threads=4
-
   clang_TSAN:
     runs-on: ubuntu-latest
     container: ghcr.io/nascheme/numpy-tsan:3.14t