add missing alt text to some <img> tags (#3903)

frontend/components/badge-examples.tsx

@@ -92,7 +92,12 @@ function Example({
     <tr>
       <ClickableTh onClick={handleClick}>{title}:</ClickableTh>
       <td>
-        <Badge clickable onClick={handleClick} src={previewUrl} />
+        <Badge
+          alt={`${title} badge`}
+          clickable
+          onClick={handleClick}
+          src={previewUrl}
+        />
       </td>
       <td>
         <ClickableCode onClick={handleClick}>{exampleUrl}</ClickableCode>

frontend/components/customizer/customizer.js

@@ -56,7 +56,7 @@ export default function Customizer({
     }
     return (
       <p>
-        <Badge display="block" src={src} />
+        <Badge alt="preview badge" display="block" src={src} />
       </p>
     )
   }