MDL-83561 format_social: Limit visible sections in social

* Only the first section is visible in social format, so we
limit the visibility of the section to the first section.
This impacts the move dialog.

course/format/social/lib.php

@@ -170,4 +170,18 @@ public function get_max_sections() {
         // Social ony uses one section.
         return 1;
     }
+
+    /**
+     * Returns if an specific section is visible to the current user.
+     *
+     * Formats can overrride this method to implement any special section logic.
+     *
+     * @param section_info $section the section modinfo
+     * @return bool;
+     */
+    #[\Override]
+    public function is_section_visible(section_info $section): bool {
+        $visible = parent::is_section_visible($section);
+        return $visible && $section->section == 0;
+    }
 }