sagemathgh-39074: Fix the issue number format in deprecation comment

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Fixes a typo in the developer guide, noted in
sagemath#38207 (comment).

### 📝 Checklist

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- [ ] I have updated the documentation and checked the documentation
preview.

### ⌛ Dependencies

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

build/pkgs/configure/checksums.ini

@@ -1,3 +1,3 @@
 tarball=configure-VERSION.tar.gz
-sha1=62eedaff4c03b55fdd6f8e1242026226adbf3a16
-sha256=54036d6435218ce1daa7d5d512e1bfd74d3713ed5745d5c49ee1f5e6122a25de
+sha1=281536743d90c17bd35976ebdfb41dd37ddf70fe
+sha256=765ef990d39e231579c0423441d77cb37c3a436fc55f307e963ff3983124d3a7

build/pkgs/configure/package-version.txt

@@ -1 +1 @@
-f6ad0ecf1f4a269f5954d5487336b13f70624594
+0fdf86888a3a1d03d9e7785ee10521ceb0d48faf

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: