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



diff --git a/Doc/library/enum.rst b/Doc/library/enum.rst
index a0b078c..c532e2c 100644
--- a/Doc/library/enum.rst
+++ b/Doc/library/enum.rst
@@ -61,7 +61,7 @@
     the bitwise operations without losing their :class:`Flag` membership.
 
 .. function:: unique
-   :noindex:
+    :noindex:
 
     Enum class decorator that ensures only one name is bound to any one value.