SelectPanel: add role=combobox to filter input (#4977)

* add role=combobox to filter input

* Create selectpanel-combobox.md

Author: siddharthkp

.changeset/green-poems-play.md

@@ -0,0 +1,5 @@
+---
+"@primer/react": patch
+---
+
+SelectPanel: Add `role=combobox` to filter input (behind feature flag `primer_react_select_panel_with_modern_action_list`)

packages/react/src/FilteredActionList/FilteredActionListWithModernActionList.tsx

@@ -138,8 +138,11 @@ export function FilteredActionList({
           onChange={onInputChange}
           onKeyPress={onInputKeyPress}
           placeholder={placeholderText}
-          aria-label={placeholderText}
+          role="combobox"
+          aria-expanded="true"
+          aria-autocomplete="list"
           aria-controls={listId}
+          aria-label={placeholderText}
           aria-describedby={inputDescriptionTextId}
           {...textInputProps}
         />