Make trust handler use ensure_async

Author: vidartf

jupyter_server/services/contents/handlers.py

@@ -294,7 +294,7 @@ class TrustNotebooksHandler(JupyterHandler):
     @web.authenticated
     async def post(self,path=''):
         cm = self.contents_manager
-        await cm.trust_notebook(path)
+        await ensure_async(cm.trust_notebook(path))
         self.set_status(201)
         self.finish()
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