### Preflight Checklist

- [X] I have read the [Contributing Guidelines](https://github.com/electron/electron/blob/master/CONTRIBUTING.md) for this project.
- [X] I agree to follow the [Code of Conduct](https://github.com/electron/electron/blob/master/CODE_OF_CONDUCT.md) that this project adheres to.
- [X] I have searched the [issue tracker](https://www.github.com/electron/electron/issues) for a feature request that matches the one I want to file, without success.

### Electron Version

14.0.0

### What operating system are you using?

Ubuntu

### Operating System Version

Ubuntu 18.04

### What arch are you using?

x64

### Last Known Working Electron version

13.1.7

### Expected Behavior

The buttons in a (native) file dialog read "Cancel"  and "OK"

### Actual Behavior

The buttons in a native file dialog read `gtk-cancel` and `gtk-ok`.

### Testcase Gist URL

https://gist.github.com/Kilian/3de5f404d90d9b12ccaec817fdc4d6da

### Additional Information

Main window has a file input, click it to open the File chooser. Test on Ubuntu between 14.x and 13.x to see the difference. Probably caused by https://github.com/electron/electron/pull/19159

Electron 13.1.7:
![Selection_999(158)](https://user-images.githubusercontent.com/41970/126761063-a5361b8f-d057-406e-bb45-c71d48224b16.png)

Electron 14.0.0-beta.16
![Selection_999(156)](https://user-images.githubusercontent.com/41970/126761068-d6377aee-79f9-47a8-a3b5-f2a96578fda8.png)

shell/browser/ui/message_box_gtk.cc
auto it = GetDialogsMap().find(id);
  if (it == GetDialogsMap().end()) {
    LOG(ERROR) << "CloseMessageBox called with nonexistent ID";
    return;
  }
  gtk_window_close(GTK_WINDOW(it->second));
}
void ShowErrorBox(const std::u16string& title, const std::u16string& content) {
  if (Browser::Get()->is_ready()) {
    electron::MessageBoxSettings settings;
    settings.type = electron::MessageBoxType::kError;
    settings.buttons = {};
    settings.title = "Error";
    settings.message = base::UTF16ToUTF8(title);
    settings.detail = base::UTF16ToUTF8(content);
    GtkMessageBox(settings).RunSynchronous();
  } else {
    fprintf(stderr,
            ANSI_TEXT_BOLD ANSI_BACKGROUND_GRAY ANSI_FOREGROUND_RED
            "%s\n" ANSI_FOREGROUND_BLACK "%s" ANSI_RESET "\n",
            base::UTF16ToUTF8(title).c_str(),
            base::UTF16ToUTF8(content).c_str());
  }
}
}