Update userdocs/diagnostics/clang-declaration-import.md

Co-authored-by: Becca Royal-Gordon <[email protected]>

Author: tshortli

userdocs/diagnostics/clang-declaration-import.md

@@ -10,7 +10,7 @@ typedef int NotificationIdentifier
     __attribute__((swift_name("Notification.Identifier")))
 ```
 
-The Swift compiler would emit the following warning if no type named `Notification` could not be found:
+The Swift compiler would emit the following warning if no type named `Notification` could be found:
 
 ```
 warning: imported declaration 'NotificationIdentifier' could not be mapped to 'Notification.Identifier’