Bugfix. Fix lit error complaining about invalid `@load` value

package-lock.json

@@ -10544,6 +10544,7 @@
       }
     },
     "src/headless": {
+      "name": "@converse/headless",
       "version": "10.1.7",
       "license": "MPL-2.0",
       "dependencies": {

src/shared/directives/image.js

@@ -22,7 +22,7 @@ class ImageDirective extends AsyncDirective {
                 src="${src}"
                 @click=${onClick}
                 @error=${() => this.onError(src, href, onLoad, onClick)}
-                @load=${onLoad}/></a>`;
+                @load="${onLoad}"/></a>`;
     }
 
     onError (src, href, onLoad, onClick) {