Fix FS3264 in ValueTaskOptionCE.fs

Author: tw0po1nt

src/FsToolkit.ErrorHandling/TaskValueOptionCE.fs

@@ -237,12 +237,11 @@ type TaskValueOptionBuilder() =
                         if step then
                             sm.Data.SetResult()
                         else
-                            let mutable awaiter =
-                                sm.ResumptionDynamicInfo.ResumptionData
-                                :?> ICriticalNotifyCompletion
-
-                            // assert not (isNull awaiter)
-                            sm.Data.MethodBuilder.AwaitUnsafeOnCompleted(&awaiter, &sm)
+                            match sm.ResumptionDynamicInfo.ResumptionData with
+                            | :? ICriticalNotifyCompletion as awaiter ->
+                                let mutable awaiter = awaiter
+                                sm.Data.MethodBuilder.AwaitUnsafeOnCompleted(&awaiter, &sm)
+                            | awaiter -> assert not (isNull awaiter)
 
                     with exn ->
                         savedExn <- exn