[Ignore] Update Notebook dts (#2859)

Co-authored-by: TylerLeonhardt <TylerLeonhardt@users.noreply.github.com>

Author: github-actions[bot]

vscode.proposed.d.ts

@@ -218,6 +218,7 @@ declare module 'vscode' {
 		readonly fileName: string;
 		readonly viewType: string;
 		readonly isDirty: boolean;
+		readonly isUntitled: boolean;
 		readonly cells: NotebookCell[];
 		languages: string[];
 		displayOrder?: GlobPattern[];