fix: scope sidebar button margin to primary website button

The .event-detail-sidebar__card wa-button rule was leaking onto the
supplementary link buttons, doubling their spacing on top of the gap
and top border on the surrounding list.

Author: mattobee

src/pages/events/[slug].astro

@@ -385,6 +385,7 @@ const jsonLd = {
                     variant="neutral"
                     appearance="accent"
                     style="width: 100%;"
+                    class="event-detail-sidebar__website-button"
                   >
                     Event website
                     <span class="sr-only"> (opens external site)</span>
@@ -622,7 +623,7 @@ const jsonLd = {
     font-size: var(--p-step--1);
   }
 
-  .event-detail-sidebar__card wa-button {
+  .event-detail-sidebar__website-button {
     margin-top: var(--p-space-xs);
   }