Use warning tray icon when reboot is required

Prioritize the 'reboot required' icon over 'available updates' according
to mtwebster's feedback and continue informing if there are selected
updates.

Also align with the opening delimiter, based on PEP8 style guide.
Reference: https://peps.python.org/pep-0008/#indentation

Co-authored-by: Michael Webster <miketwebster@gmail.com>

Author: randomnoise

usr/lib/linuxmint/mintUpdate/mintUpdate.py

@@ -639,12 +639,13 @@ def show_error(self, error_msg):
 
     @_idle
     def show_updates_in_UI(self, num_visible, num_software, num_security, download_size, is_self_update, model_items):
+        status_string = ""
+
         if num_visible > 0:
             self.logger.write("Found %d software updates" % num_visible)
             if is_self_update:
                 self.ui_stack.set_visible_child_name("self_update_page")
                 self.ui_statusbar.set_visible(False)
-                status_string = ""
                 details = []
 
                 for item in model_items:
@@ -660,13 +661,19 @@ def show_updates_in_UI(self, num_visible, num_software, num_security, download_s
                 self.ui_install_button.set_sensitive(True)
                 self.ui_window.set_sensitive(True)
             systray_tooltip = gettext.ngettext("%d update available", "%d updates available", num_visible) % num_visible
-            self.set_status(status_string, systray_tooltip, "mintupdate-updates-available-symbolic", True)
+
+            if not self.reboot_required:
+                self.set_status(status_string, systray_tooltip, "mintupdate-updates-available-symbolic", True)
         else:
             self.logger.write("System is up to date")
             self.ui_stack.set_visible_child_name("success_page")
-            self.set_status("", _("Your system is up to date"), "mintupdate-up-to-date-symbolic",
-                                        not self.settings.get_boolean("hide-systray"))
 
+            if not self.reboot_required:
+                self.set_status("", _("Your system is up to date"), "mintupdate-up-to-date-symbolic",
+                                not self.settings.get_boolean("hide-systray"))
+
+        if self.reboot_required:
+            self.set_status(status_string, _("Reboot required"), "mintupdate-warning-symbolic", True)
 
         self.ui_notebook_details.set_current_page(0)