Change icon SVG imports to use a default import (#28709)

app/javascript/__mocks__/svg.js

@@ -1,3 +1,3 @@
-// eslint-disable-next-line import/no-anonymous-default-export
-export default 'SvgrURL';
-export const ReactComponent = 'div';
+const ReactComponent = 'div';
+
+export default ReactComponent;