Update MediaTypeNames+Image.xml (#10366)

Fix casing of WebP from WEBP to WebP.

Author: vanillajonathan

xml/System.Net.Mime/MediaTypeNames+Image.xml

@@ -285,7 +285,7 @@
         <ReturnType>System.String</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>Specifies that the <see cref="T:System.Net.Mime.MediaTypeNames.Image" /> data is in WEBP format.</summary>
+        <summary>Specifies that the <see cref="T:System.Net.Mime.MediaTypeNames.Image" /> data is in WebP format.</summary>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>