Update pipeline python-client

Author: chillaq

.harness/orgs/PROD/projects/Harness_Split/pipelines/pythonclient.yaml

@@ -106,6 +106,7 @@ pipeline:
 
                       # Run pytest with JUnit XML report output
                       cd /harness
+                      pip install Cython
                       pip install aiohttp==3.8.4
                       pip install cryptography==45.0.7
                       pip install pycparser==2.21