gh-39074: Fix the issue number format in deprecation comment
    
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Fixes a typo in the developer guide, noted in
#38207 (comment).

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URL: #39074
Reported by: Kwankyu Lee
Reviewer(s): Frédéric Chapoton

Author: Release Manager

src/doc/en/developer/coding_in_python.rst

@@ -786,13 +786,13 @@ the procedure below:
     class NewClass:
         ...
 
-    OldClass = NewClass   # OldClass is deprecated. See Issue 12345.
+    OldClass = NewClass   # OldClass is deprecated. See Issue #12345.
 
 * **Removing a class:**  add a comment:
 
   .. CODE-BLOCK:: python
 
-    # OldClass is deprecated. See Issue 12345.
+    # OldClass is deprecated. See Issue #12345.
 
     class OldClass: