fix(ui5-avatar-group): disable pointer events on overflow button in Group Mode (#11935)

- Problem
Overflow button was receiving focus in Group mode, preventing group click events from firing when clicked.

- Solution
Add pointer-events: none to the overflow button to not receive focus upon clicking when type="Group"

Fixes: #11866

Author: NakataCode

packages/main/src/themes/AvatarGroup.css

@@ -36,7 +36,8 @@
 }
 
 :host([type="Group"]) ::slotted([ui5-button]),
-:host([type="Group"]) ::slotted([ui5-avatar]) {
+:host([type="Group"]) ::slotted([ui5-avatar]),
+:host([type="Group"]) .ui5-avatar-group-overflow-btn {
 	pointer-events: none;
 }