Typo in StringBuilder.xml (#4401)

Author: danmoseley

xml/System.Text/StringBuilder.xml

@@ -4077,7 +4077,7 @@ The purpose of this method is to efficiently extract the data of a *constant* <x
 
 The <xref:System.ReadOnlyMemory%601> chunks returned are not guaranteed to remain unchanged if the <xref:System.Text.StringBuilder> is modified, so do not cache them for later use.
 
-Creating a <xref:System.ReadOnlySpan%601> from a <xref:System.ReadOnlyMemory%601> (as the <xref:System.ReadOnlyMemory%601.Span?displayProperty=nameWithType> method does in the previous example, is expensive, so create a local variable for the span if you need to use it in a nested `for` statement. For example:
+Creating a <xref:System.ReadOnlySpan%601> from a <xref:System.ReadOnlyMemory%601> (as the <xref:System.ReadOnlyMemory%601.Span?displayProperty=nameWithType> method does in the previous example) is expensive, so create a local variable for the span if you need to use it in a nested `for` statement. For example:
 
 ```csharp
 foreach (ReadOnlyMemory<char> chunk in sb.GetChunks())