Update background size

Update background size property to `contain` so that the whole image shows

(cherry picked from commit 215ef3d)

Author: matthewcare

src/Umbraco.Web.UI.Client/src/views/components/blockcard/umb-block-card.less

@@ -58,7 +58,7 @@ umb-block-card {
         padding-bottom: 10/16*100%;
         background-color: @gray-12;
 
-        background-size: cover;
+        background-size: contain;
         background-position: 50% 50%;
         background-repeat: no-repeat;