fix(core): override LinkedDocBlockComponent initial state (#8253)

Upstreams: toeverything/blocksuite#8354

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packages/frontend/core/src/components/blocksuite/block-suite-editor/specs/custom/spec-patchers.tsx

@@ -484,10 +484,12 @@ export function patchEdgelessClipboard() {
 }
 
 @customElement('affine-linked-doc-ref-block')
-// @ts-expect-error ignore private warning for overriding _load
 export class LinkedDocBlockComponent extends EmbedLinkedDocBlockComponent {
-  override async _load() {
-    this.isBannerEmpty = true;
+  override getInitialState() {
+    return {
+      loading: false,
+      isBannerEmpty: true,
+    };
   }
 }