Implement the proposed fix from issue #1290 (#1499)

* Implement the proposed fix from issue #1290

#1290

Without this change, if strict type checking is enabled, usages of a `@unmanaged()` decorator cause the following error:

```
Argument of type 'undefined' is not assignable to parameter of type 'string'.
```

* Empty commit to nudge CI

src/annotation/unmanaged.ts

@@ -3,7 +3,7 @@ import { Metadata } from '../planning/metadata';
 import { tagParameter, DecoratorTarget } from './decorator_utils';
 
 function unmanaged() {
-  return function (target: DecoratorTarget, targetKey: string, index: number) {
+  return function (target: DecoratorTarget, targetKey: string | undefined, index: number) {
     const metadata = new Metadata(METADATA_KEY.UNMANAGED_TAG, true);
     tagParameter(target, targetKey, index, metadata);
   };