sysupdate: change status once operation has completed

Otherwise after the service exits it will still show
"Installing 'foobar'" as the status, which is confusing

(cherry picked from commit 5cfc9c34f4a38cc82c233e453373d48231944d81)
(cherry picked from commit 0e502d986b724f195385ad99f7f214d8586fec7f)
(cherry picked from commit 8d7dce9a534cf14a2587145590ddea01eeb84291)

Author: bluca

src/sysupdate/sysupdate.c

@@ -832,6 +832,9 @@ static int context_apply(
 
         log_info("%s Successfully installed update '%s'.", special_glyph(SPECIAL_GLYPH_SPARKLES), us->version);
 
+        (void) sd_notifyf(/* unset_environment=*/ false,
+                          "STATUS=Installed '%s'.", us->version);
+
         if (ret_applied)
                 *ret_applied = us;