update test for new expander's soirce reporting

A case could be made that the "eval" source is bogus, and it was
better to omit it. But the new expander's source reporting is more
consistent, as reflected by the fact that "eval" shows up in a syntax
error with both the old and new expanders.

scribble-test/tests/scribble/docs/stxobj.txt

@@ -1,2 +1,2 @@
-  > (syntax-e #'(+ 1 2))                            
-  '(#<syntax:1:0 +> #<syntax:1:0 1> #<syntax:1:0 2>)
+  > (syntax-e #'(+ 1 2))                                           
+  '(#<syntax:eval:1:0 +> #<syntax:eval:1:0 1> #<syntax:eval:1:0 2>)