Skip assertion in readline test if Readline version is 4.3

Previously, the entire method was not run for Readline 4.3, probably
because it was known to fail. Commit
c754e979d3 removed the check for
Readline 4.3.  Other than this one assertion, which also doesn't
work when using Reline, the method runs correctly when using
Readline 4.3.

Fixes [Bug #15853].

test/readline/test_readline.rb

@@ -405,7 +405,9 @@ module BasetestReadline
           line = Readline.readline("> ")
           assert_equal("hello world", line)
         end
-        if !defined?(Reline) or Readline != Reline # Reline's rendering logic is tricky
+        # Readline 4.3 doesn't include inserted text or input
+        # Reline's rendering logic is tricky
+        if Readline::VERSION != '4.3' and (!defined?(Reline) or Readline != Reline)
           assert_equal("> hello world\n", stdout.read)
         end
         stdout.close