test-org-table: Replace hline lhs expression in table formula

* testing/lisp/test-org-table.el: Replace hline lhs expression in table
  formula with relative row expression.

This fixes a test fail introduced by a2c71a6e35.  The failing test
does not check relative hline references, so it should not rely on
undocumented behaviour.

testing/lisp/test-org-table.el

@@ -421,7 +421,7 @@ reference (with row).  Mode string N."
 "
    1
    ;; Compare field reference ($1) with field reference (@1)
-   "#+TBLFM: @I$<<..@>$> = if(\"$1\" == \"@1\", x, string(\"\")); E"
+   "#+TBLFM: @<<$<<..@>$> = if(\"$1\" == \"@1\", x, string(\"\")); E"
    ;; Compare field reference ($1) with absolute term
    (concat "#+TBLFM: "
 	   "$2 = if(\"$1\" == \"(0)\"   , x, string(\"\")); E :: "