Tests: Increase time to run all cells to make tests more robust

Increase waiting time and add sleep when a notebook is restarted. The
notebook is sometimes run before jupyter has finished loading everything
in the background.

Author: agoscinski

tests/conftest.py

@@ -143,7 +143,7 @@ def _selenium_driver(nb_path):
         #    )
         # )
         restart_kernel_button = None
-        waiting_time = 10
+        waiting_time = 20
         start = time.time()
 
         while restart_kernel_button is None and time.time() - start < waiting_time:
@@ -219,6 +219,7 @@ def _selenium_driver(nb_path):
                 (By.CLASS_NAME, "jp-Notebook-ExecutionIndicator"), "data-status", "idle"
             )
         )
+        time.sleep(1)
 
         return selenium