Improve AvatarStack when hovering (#2228)

* Add rounded corners to `AvatarStack-body`

* Create brave-turtles-design.md

* Lint

Author: simurai

.changeset/brave-turtles-design.md

@@ -0,0 +1,5 @@
+---
+"@primer/css": patch
+---
+
+Improve `AvatarStack` when hovering

src/avatars/avatar-stack.scss

@@ -22,6 +22,8 @@
 .AvatarStack-body {
   display: flex;
   background: var(--color-canvas-default);
+  // stylelint-disable-next-line primer/borders
+  border-radius: 100px;
 
   .avatar {
     position: relative;