Disable StartupNotify to fix alt-tabbing in GNOME

Having [`StartupNotify` set to true in the `.desktop` file](https://github.com/flathub/com.visualstudio.code/blob/master/com.visualstudio.code.desktop#L8) is causing [problems with mutter](https://gitlab.gnome.org/GNOME/mutter/-/issues/2689) where you can't alt-tab to the application until it has timed out.

Would it be possible to set it to `false`? [Upstream Code seems to do the same.](https://github.com/microsoft/vscode/blob/main/resources/linux/code.desktop#L8)

There is also [a secondary desktop file](https://github.com/flathub/com.visualstudio.code/blob/master/com.visualstudio.code-url-handler.desktop) which might need the same treatment.

Thanks!

将 com.visualstudio.code.desktop 和 com.visualstudio.code-url-handler.desktop 与 issue 中链接的上游 Code desktop 文件进行比较。将相关文件中的 StartupNotify 设置更新为 false，然后验证两个 desktop 条目都包含预期值，并且 alt-tab 超时行为已得到处理。

由索引模型根据 Issue 内容生成。