test(aria-allowed-role): cover button element widget roles (#5250)

Just adds the `aria-allowed-role` integration cases for the `<button>`
element (`separator`, `slider`, `treeitem`; `gridcell` was already
covered), which is all #4142 needs on top of #4398.

Closes #4142

---------

Co-authored-by: Steven Lambert <2433219+straker@users.noreply.github.com>

Author: chutchins25

test/integration/rules/aria-allowed-role/aria-allowed-role.html

@@ -213,6 +213,9 @@ <h1 id="pass-h1-valid-role" role="none"></h1>
   title="IconCheckmark"
   aria-label="IconCheckmark icon"
 ></button>
+<button id="pass-button-role-separator" role="separator"></button>
+<button id="pass-button-role-slider" role="slider"></button>
+<button id="pass-button-role-treeitem" role="treeitem"></button>
 
 <dd id="fail-dd-no-role" role="link"></dd>
 <dt id="fail-dt-no-role" role="banner"></dt>

test/integration/rules/aria-allowed-role/aria-allowed-role.json

@@ -90,7 +90,10 @@
     ["#pass-navnone-1"],
     ["#pass-navnone-2"],
     ["#pass-search-elm"],
-    ["#pass-button-role-gridcell"]
+    ["#pass-button-role-gridcell"],
+    ["#pass-button-role-separator"],
+    ["#pass-button-role-slider"],
+    ["#pass-button-role-treeitem"]
   ],
   "violations": [
     ["#fail-dd-no-role"],