Fix spelling of method (#4301)

Author: Boaz101

xml/System.Buffers.Text/Utf8Formatter.xml

@@ -25,7 +25,7 @@
   </Base>
   <Interfaces />
   <Docs>
-    <summary>Provides static mthods to format common data types as Utf8 strings.</summary>
+    <summary>Provides static methods to format common data types as Utf8 strings.</summary>
     <remarks>To be added.</remarks>
   </Docs>
   <Members>