A11y - Fix label for Settings Button

Change-Id: Ia71f593c2aff5573c9935f4a269dd62a9bc447da
diff --git a/polygerrit-ui/app/elements/core/gr-main-header/gr-main-header_html.js b/polygerrit-ui/app/elements/core/gr-main-header/gr-main-header_html.js
index 19e833c..2e64b3b 100644
--- a/polygerrit-ui/app/elements/core/gr-main-header/gr-main-header_html.js
+++ b/polygerrit-ui/app/elements/core/gr-main-header/gr-main-header_html.js
@@ -221,6 +221,8 @@
           class="settingsButton"
           href$="[[_generateSettingsLink()]]"
           title="Settings"
+          aria-label="Settings"
+          role="button"
         >
           <iron-icon icon="gr-icons:settings"></iron-icon>
         </a>