Use AccessibleImage component instead of img in Workers (firefox-devtools#7639)

Author: kenjiO

.eslintrc.jsx-a11y

@@ -10,7 +10,7 @@
     // plugin:jsx-a11y/recommended set (which they override) that has different severity
     // levels.
     "jsx-a11y/accessible-emoji": "warn",
-    "jsx-a11y/alt-text": "warn",
+    "jsx-a11y/alt-text": "error",
     "jsx-a11y/anchor-has-content": "warn",
     "jsx-a11y/anchor-is-valid": "error",
     "jsx-a11y/aria-activedescendant-has-tabindex": "warn",

src/components/SecondaryPanes/Workers.js

@@ -45,7 +45,7 @@ export class Workers extends Component<Props> {
           key={worker.actor}
           onClick={() => this.props.selectThread(worker.actor)}
         >
-          <img className="domain" />
+          <AccessibleImage className="domain" />
           {(worker.url
             ? `${this.props.getWorkerDisplayName(worker.actor)}: ${basename(
                 worker.url