Docs: missing deprecated callout for list-group-item-variant() mixin

Author: julien-deramond

scss/mixins/_list-group.scss

@@ -1,6 +1,5 @@
 @include deprecate("`list-group-item-variant()`", "v5.3.0", "v6.0.0");
 
-
 // List Groups
 
 // scss-docs-start list-group-mixin

site/content/docs/5.3/components/list-group.md

@@ -319,6 +319,8 @@ As part of Bootstrap's evolving CSS variables approach, list groups now use loca
 
 ### Sass mixins
 
+{{< deprecated-in "5.3.0" >}}
+
 Used in combination with `$theme-colors` to generate the [contextual variant classes](#variants) for `.list-group-item`s.
 
 {{< scss-docs name="list-group-mixin" file="scss/mixins/_list-group.scss" >}}