gh-35852: Fix typos on the link to the walkthrough.html
    
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### 📚 Description

In order for the link to work properly, the link
"https://doc.sagemath.org/html/en/developer/walk_through.html#chapter-
walkthrough" should be changed to
"https://doc.sagemath.org/html/en/developer/walkthrough.html#chapter-
walkthrough".
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- [ ] I have updated the documentation accordingly.

### ⌛ Dependencies

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URL: #35852
Reported by: JunheeLee
Reviewer(s): Marc Mezzarobba

Author: Release Manager

src/doc/en/installation/index.rst

@@ -25,7 +25,7 @@ macOS
 
     Obtain the SageMath sources via ``git`` as described in `The Sage
     Developer's Guide
-    <https://doc.sagemath.org/html/en/developer/walk_through.html#chapter-walkthrough>`_.
+    <https://doc.sagemath.org/html/en/developer/walkthrough.html#chapter-walkthrough>`_.
 
     - Then build SageMath from source as described in section
       :ref:`sec-installation-from-sources`.
@@ -93,7 +93,7 @@ Linux
 
     Obtain the SageMath sources via ``git`` as described in `The Sage
     Developer's Guide
-    <https://doc.sagemath.org/html/en/developer/walk_through.html#chapter-walkthrough>`_.
+    <https://doc.sagemath.org/html/en/developer/walkthrough.html#chapter-walkthrough>`_.
 
     - Then build SageMath from source as described in section
       :ref:`sec-installation-from-sources`.