`Node.getRootNode` does not work correctly unless it attached to the `document`

[mozesstumpf]

Describe the bug
Node.getRootNode({ composed: false }) retunrs the Node itself instead of the ShadowRoot if we do not add the ShadowRoot into the document.

To Reproduce

import { expect, test } from "vitest";

test("ShadowRoot", () => {
	const host = document.createElement("div");
	const child = document.createElement("span");

	const shadowRoot = host.attachShadow({ mode: "open" });

	shadowRoot.append(child);

	// It works if we uncomment this line
	// document.body.append(host);

	// It becomes a span if the `host` is not added to the `document`
	const root = child.getRootNode({ composed: false }); // Supposed to return the ShadowRoot

	expect(root).toBe(shadowRoot);
});

Expected behavior
Test should be passed