Another spelling fix.

Author: hjoliver

cylc/flow/cfgspec/workflow.py

@@ -1130,7 +1130,7 @@ def get_script_common_text(this: str, example: Optional[str] = None):
                       # "a" may either succeed or fail
                       completion = succeeded or failed
 
-                   Which could be fixed by ammending the graph like so:
+                   Which could be fixed by amending the graph like so:
 
                    .. code-block:: cylc-graph