[doc] Fix a few margins due to bad markup (GH-23619)



diff --git a/Doc/library/os.rst b/Doc/library/os.rst
index ab1a615..35cf7c0 100644
--- a/Doc/library/os.rst
+++ b/Doc/library/os.rst
@@ -1323,12 +1323,12 @@
 
 .. data:: RWF_APPEND
 
-    Provide a per-write equivalent of the :data:`O_APPEND` :func:`os.open`
-    flag. This flag is meaningful only for :func:`os.pwritev`, and its
-    effect applies only to the data range written by the system call. The
-    *offset* argument does not affect the write operation; the data is always
-    appended to the end of the file. However, if the *offset* argument is
-    ``-1``, the current file *offset* is updated.
+   Provide a per-write equivalent of the :data:`O_APPEND` :func:`os.open`
+   flag. This flag is meaningful only for :func:`os.pwritev`, and its
+   effect applies only to the data range written by the system call. The
+   *offset* argument does not affect the write operation; the data is always
+   appended to the end of the file. However, if the *offset* argument is
+   ``-1``, the current file *offset* is updated.
 
    .. availability:: Linux 4.16 and newer.