Update empty state btn margin

**Why?**

Pajamas says so

https://gitlab.com/gitlab-org/gitlab/-/merge_requests/24764#note_285522493

app/assets/stylesheets/framework/blocks.scss

@@ -325,11 +325,11 @@
   }
 
   .btn {
-    margin: $btn-side-margin 5px;
+    margin: $gl-padding-8 $gl-padding-4;
 
     @include media-breakpoint-down(xs) {
       width: 100%;
-      margin: $btn-side-margin 0;
+      margin: $gl-padding-8 0;
     }
   }
 }

changelogs/unreleased/fe-update-empty-state-btn-x-margin.yml

+---
+title: Update button margin of various empty states
+merge_request: 24806
+author:
+type: other