Missing return value in MemoryExtensions.Trim (#2839)

Author: carlossanlop

xml/System/MemoryExtensions.xml

@@ -3396,7 +3396,7 @@ If `culture` is `null`, <xref:System.Globalization.CultureInfo.CurrentCulture?di
       <Docs>
         <param name="memory">The source memory from which the characters are removed.</param>
         <summary>Removes all leading and trailing whitespace characters from a read-only character memory region.</summary>
-        <returns>To be added.</returns>
+        <returns>The trimmed character memory region.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>