guard against strange behaviour of OverloadedReturnType in pre 5.3 versions

Author: EskiMojo14

packages/toolkit/src/tsHelpers.ts

@@ -224,18 +224,20 @@ export function asSafePromise<Resolved, Rejected>(
   return promise.catch(fallback) as SafePromise<Resolved | Rejected>
 }
 
+type NotUnknown<T> = IsUnknown<T, never, T>
+
 export type OverloadedReturnType<Fn extends (...args: any[]) => any> =
   Fn extends {
-    (...args: any): infer R1
-    (...args: any): infer R2
-    (...args: any): infer R3
+    (...args: any[]): infer R1
+    (...args: any[]): infer R2
+    (...args: any[]): infer R3
   }
-    ? R1 | R2 | R3
+    ? NotUnknown<R1> | NotUnknown<R2> | NotUnknown<R3>
     : Fn extends {
-          (...args: any): infer R1
-          (...args: any): infer R2
+          (...args: any[]): infer R1
+          (...args: any[]): infer R2
         }
-      ? R1 | R2
+      ? NotUnknown<R1> | NotUnknown<R2>
       : ReturnType<Fn>
 
 export type Increment<