Disable a type safety/correctness assertion

In `CoreObject.create()`, we currently have an unsafe cast when
constructing an instance with props, because the code assumes one of
two things. Either: the `factory` is always set, *or* it is safe to
call `setFactoryFor` with `undefined`. A number of acceptance tests are
(incorrectly? Unclear!) relying on the ability to run through this path
with `factory` being `undefined`. It's *possible* that actually means
that the type for `setFactoryFor` should allow `undefined`, but we
typed it the other way for good reason! Accordingly, this *casts*
`factory`, and the commented-out `assert()` is here in the hope that we
can enable it after addressing tests in the future.

packages/@ember/object/core.ts

@@ -768,9 +768,17 @@ class CoreObject {
 
     if (props !== undefined) {
       instance = new this(getOwner(props));
+      // TODO(SAFETY): at present, we cannot actually rely on this being set,
+      // because a number of acceptance tests are (incorrectly? Unclear!)
+      // relying on the ability to run through this path with `factory` being
+      // `undefined`. It's *possible* that actually means that the type for
+      // `setFactoryFor()` should allow `undefined`, but we typed it the other
+      // way for good reason! Accordingly, this *casts* `factory`, and the
+      // commented-out `assert()` is here in the hope that we can enable it
+      // after addressing tests *or* updating the call signature here.
       let factory = getFactoryFor(props);
-      assert(`missing factory when creating object ${instance}`, factory !== undefined);
-      setFactoryFor(instance, factory);
+      // assert(`missing factory when creating object ${instance}`, factory !== undefined);
+      setFactoryFor(instance, factory as NonNullable<typeof factory>);
     } else {
       instance = new this();
     }