Issue #3275451: Add save to library link to the built section preserve array key

src/SectionLibraryRender.php

@@ -82,6 +82,7 @@ class SectionLibraryRender implements TrustedCallbackInterface {
         elseif (isset($section['configure']) && isset($section['configure']['#url'])) {
           $params = $section['configure']['#url']->getRouteParameters();
           // Pop the last item to add the link before it.
+          $last_item_section_key = array_key_last($sections[$key]);
           $last_item_section = array_pop($sections[$key]);
           $add_to_library_url = Url::fromRoute(
             'section_library.add_section_to_library',
@@ -109,7 +110,7 @@ class SectionLibraryRender implements TrustedCallbackInterface {
             '#access' => $add_to_library_url->access(),
           ];
           // Push the last item again.
-          array_push($sections[$key], $last_item_section);
+          $sections[$key][$last_item_section_key] = $last_item_section;
         }
       }