Fix typo and indentation

Author: pablogsal

garbage_collector.rst

@@ -399,12 +399,12 @@ word-aligned addresses end in ``000``, leaving the last 3 bits available.
 The CPython GC makes use of two fat pointers:
 
 * The ``_gc_prev``` field is normally used as the "previous" pointer to maintain the
-  doubly linked list but the lowest two bits of are used to keep some flags like
-  ``PREV_MASK_COLLECTING`` and ``_PyGC_PREV_MASK_FINALIZED``. Between collections, the
-  only flag that can be present is ``_PyGC_PREV_MASK_FINALIZED`` that indicates if an
-  object has been already finalized. During collections ``_gc_prev`` is temporary
-  used for storing the temporary copy of the reference count (``gc_refs``), and the
-  GC linked list becomes a singly linked list until ``_gc_prev`` is restored.
+  doubly linked list but its lowest two bits are used to keep some flags like
+  ``PREV_MASK_COLLECTING`` and ``_PyGC_PREV_MASK_FINALIZED``. Between collections,
+  the only flag that can be present is ``_PyGC_PREV_MASK_FINALIZED`` that indicates
+  if an object has been already finalized. During collections ``_gc_prev`` is
+  temporary used for storing the temporary copy of the reference count (``gc_refs``),
+  and the GC linked list becomes a singly linked list until ``_gc_prev`` is restored.
 
 * The ``_gc_next`` field is used as the "next" pointer to maintain the doubly linked
   list but during collection its lowest bit is used to keep the