DOCSP-27851: fix link to course (#76)

Author: Chris Cho

source/index.txt

@@ -64,7 +64,7 @@ Take the Free Online Course Taught by MongoDB
        .. figure:: /includes/figures/M220N.png
           :alt: Banner for the C# MongoDB University Course
 
-     - `Using MongoDB with C# <https://learn.mongodb.com/learning-paths/using-mongodb-with-c>`__
+     - `Using MongoDB with C# <https://learn.mongodb.com/learning-paths/using-mongodb-with-csharp>`__
 
        Learn the essentials of C# & ASP.NET application development with MongoDB.
 
@@ -90,4 +90,4 @@ FAQ
 ---
 
 For answers to commonly asked questions about the {+driver-long+}, see the :ref:`csharp-faq`
-section.
+section.