fix(editor): can not delete code block with delete keyboard (#11988)

blocksuite/affine/blocks/code/src/code-block.ts

@@ -332,7 +332,7 @@ export class CodeBlockComponent extends CaptionedBlockComponent<CodeBlockModel>
         return true;
       },
       Delete: () => {
-        return true;
+        return;
       },
       Enter: () => {
         this.doc.captureSync();