Issue #141: revert requirements.txt installation validation

.github/workflows/workflow-lint-test-python.yml

@@ -28,7 +28,9 @@ jobs:
         run: |
           python -m pip install --upgrade pip
           pip install ruff==0.1.0
-          pip install -r requirements.txt
+          if [ -f requirements.txt ]; then \
+            pip install -r requirements.txt; \
+          fi
           pip install pytest pytest-cov # for coverage
 
       - name: Lint with ruff