Use better assertions for computedrole (web-platform-tests#39618)

Resolves web-platform-tests#39118

Changes the WebDriver tests for computedrole to avoid some invalid tests. Note: The removed validation test are either already tests in /html-aam or /wai-aria, or are on the list to be written soon, so this should keep the WebDriver tests reliable without churn from unrelated accessibility changes.

Reviewed by juliandescottes and jcsteh.

webdriver/tests/get_computed_role/get.py

@@ -77,9 +77,9 @@ def test_stale_element_reference(session, stale_element, as_frame):
 
 
 @pytest.mark.parametrize("html,tag,expected", [
-    ("<li role=menuitem>foo", "li", "menuitem"),
+    ("<article>foo</article>", "article", "article"),
     ("<input role=searchbox>", "input", "searchbox"),
-    ("<img role=presentation>", "img", "presentation")])
+    ("<img role=button tabindex=0>", "img", "button")])
 def test_computed_roles(session, inline, html, tag, expected):
     session.url = inline(html)
     element = session.find.css(tag, all=False)