[range.split.iterator] Add indentation (#8981)

Author: hewillk

source/ranges.tex

@@ -8636,7 +8636,7 @@
     subrange<iterator_t<V>> @\exposid{next_}@ = subrange<iterator_t<V>>();          // \expos
     bool @\exposid{trailing_empty_}@ = false;                                       // \expos
     constexpr @\exposid{iterator}@(split_view& parent, iterator_t<V> current,       // \expos
-                     subrange<iterator_t<V>> next);
+                       subrange<iterator_t<V>> next);
 
   public:
     using iterator_concept = forward_iterator_tag;