CI: removed ubuntu from os matrix (covered by parallel tests)

Removed feature/parallel-ci-workflows as trigger for action

.github/workflows/pytest.yml

@@ -20,7 +20,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, windows-latest, macos-latest]
+        os: [windows-latest, macos-latest]
         python-version: ["3.11"]
     steps:
       - uses: actions/checkout@v4