Fix layout of the cards on the guidelines page

See https://hifis-review-app.hzdr.de/review-apps/hifis-hifis-net/fix-guidelines/guidelines

_includes/cards/post_card_image.html

@@ -15,7 +15,7 @@ post: The post which sould be displayed on the card
     | strip 
     | relative_url -%}
 {%- endif -%}
-<div class="card {{ include.class }}">
+<div class="card top-image-card {{ include.class }}">
     <img class="card-img-top card-img-equal" src="{{ img_url }}" alt="Title image">
     <div class="card-img-overlay">
         <span class="badge badge-secondary">