Update end-time when workflow execution is canceled

#26

app/crud/crud_workflow_execution.py

 from uuid import UUID
 
 from clowmdb.models import WorkflowExecution
-from sqlalchemy import delete, or_, select, update
+from sqlalchemy import delete, or_, select, text, update
 from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy.orm import joinedload
 
@@ -146,7 +146,7 @@ class CRUDWorkflowExecution:
         stmt = (
             update(WorkflowExecution)
             .where(WorkflowExecution._execution_id == eid)
-            .values(status=WorkflowExecution.WorkflowExecutionStatus.CANCELED.name)
+            .values(status=WorkflowExecution.WorkflowExecutionStatus.CANCELED.name, end_time=text("CURRENT_TIMESTAMP"))
         )
         await db.execute(stmt)
         await db.commit()