fix two build warnings

Author: BillWagner

docs/csharp/language-reference/keywords/extension.md

@@ -28,7 +28,7 @@ Static extensions can be called as though they're static members of the receiver
 
 :::code language="csharp" source="./snippets/extensions.cs" id="UseStaticExtensions":::
 
-> [!IMPORTANT]
+> [!IMPORTANT]  
 > An extension doesn't introduce a *scope* for member declarations. All members declared in a single class, even if in multiple extensions, must have unique signatures. The generated signature includes the receiver type in its name for static members and the receiver parameter for extension instance members.
 
 The following example shows an extension method using the `this` modifier:

docs/csharp/language-reference/keywords/snippets/ExtensionMethods.cs

@@ -26,7 +26,7 @@ public static void BasicExample()
     }
 }
 
-// <GenericExtensionMethod>
+// <GenericExtensionMethods>
 public static class GenericExtensions
 {
     public static IEnumerable<T> Spread<T>(this IEnumerable<T> source, int start, int count)
@@ -44,7 +44,7 @@ public static IEnumerable<T1> Append<T1, T2>(this IEnumerable<T1> source, IEnume
         }
     }
 
-    public static IEnumerable<T1> Prepend<T1, TArg>(this IEnumerable<T1> source, IEnumerable<T2> second, Func<T2, T1> Converter)
+    public static IEnumerable<T1> Prepend<T1, T2>(this IEnumerable<T1> source, IEnumerable<T2> second, Func<T2, T1> Converter)
     {
         foreach (T2 item in second)
         {
@@ -56,6 +56,6 @@ public static IEnumerable<T1> Prepend<T1, TArg>(this IEnumerable<T1> source, IEn
         }
     }
 }
-// </GenericExtensionMethod>
+// </GenericExtensionMethods>