Only save current value when navigated to the end (#240972)

So if you navigated up, then saveState happened, it doesn't overwrite the last value in history
Fix microsoft/vscode-copilot-release#3750

src/vs/workbench/contrib/chat/browser/chatInputPart.ts

@@ -1500,7 +1500,10 @@ export class ChatInputPart extends Disposable implements IHistoryNavigationWidge
 	}
 
 	saveState(): void {
-		this.saveCurrentValue(this.getInputState());
+		if (this.history.isAtEnd()) {
+			this.saveCurrentValue(this.getInputState());
+		}
+
 		const inputHistory = [...this.history];
 		this.historyService.saveHistory(this.location, inputHistory);
 	}