remove surplus 'an'

S07-lists.pod

@@ -293,7 +293,7 @@ argument to be bound to an C<@>-sigil parameter:
 
 This would be rather too inconvenient. Therefore, the signature binder (which
 actually uses C<::=> assignment semantics rather than C<:=>) will spot failure
-to bind the an C<@>-sigil parameter, and then check if the argument does the
+to bind the <@>-sigil parameter, and then check if the argument does the
 C<PositionalBindFailover> role. If it does, then it will call the C<cache>
 method on the argument and bind the result of that instead.