chore: fix vbind var and add alt attr

This commit addresses a typo in `buildSrcSet.vue` that resulted in an
error where `advancedSrc` was not defined in the scope of the component.
It also adds an `alt` attribute to the component, since the vue linter
was complaining about it missing.

src/components/advanced/buildSrcSet.vue

@@ -1,8 +1,9 @@
 <template>
   <img
-    :src="advancedSrc"
+    :src="advancedUrl"
     :srcset="advancedSrcSet"
     data-testid="advanced-build-src-set"
+    alt="advanced-build-srcset-fruit-image"
   />
 </template>