Fix a typo

Author: grynspan

Sources/Testing/Attachments/Test.Attachable.swift

@@ -113,7 +113,7 @@ extension Test.Attachable where Self: Collection, Element == UInt8 {
   // We do not provide an implementation of withUnsafeBufferPointer(for:_:) here
   // because there is no way in the standard library to statically detect if a
   // collection can provide contiguous storage (_HasContiguousBytes is not API.)
-  // If withContiguousBytesIfAvailable(_:) fails, we don't want to make a
+  // If withContiguousStorageIfAvailable(_:) fails, we don't want to make a
   // (potentially expensive!) copy of the collection.
 }