[3.15] Docs: Fix method directive signatures in `enum` docs (GH-151429) (#151434)

(cherry picked from commit 5b385197625e669473859c63bee6f14c983d2be6)

Co-authored-by: Jonathan Dung <jonathandung@yahoo.com>

Doc/library/enum.rst

diff --git a/Doc/library/enum.rst b/Doc/library/enum.rst
index be7f59b..d2ebbe4 100644
--- a/Doc/library/enum.rst
+++ b/Doc/library/enum.rst
@@ -629,7 +629,7 @@
          >>> white in purple
          False
 
-   .. method:: __iter__(self):
+   .. method:: __iter__(self)
 
       Returns all contained non-alias members::
 
@@ -640,7 +640,7 @@
 
       .. versionadded:: 3.11
 
-   .. method:: __len__(self):
+   .. method:: __len__(self)
 
       Returns number of members in flag::
 
@@ -651,7 +651,7 @@
 
       .. versionadded:: 3.11
 
-   .. method:: __bool__(self):
+   .. method:: __bool__(self)
 
       Returns *True* if any members in flag, *False* otherwise::
 
@@ -688,7 +688,7 @@
          >>> purple ^ Color.GREEN
          <Color.RED|GREEN|BLUE: 7>
 
-   .. method:: __invert__(self):
+   .. method:: __invert__(self)
 
       Returns all the flags in *type(self)* that are not in *self*::