Skip tests that are failing on TruffleRuby (#1170)

Author: st0012

test/irb/test_pager.rb

@@ -54,6 +54,8 @@ def test_overflow
     end
 
     def test_callback_delay
+      omit if RUBY_ENGINE == "truffleruby"
+
       actual_events = []
       overflow_callback = ->(lines) do
         actual_events << [:callback_called, lines]

test/irb/test_ruby_lex.rb

@@ -14,6 +14,8 @@ def teardown
     end
 
     def test_interpolate_token_with_heredoc_and_unclosed_embexpr
+      omit if RUBY_ENGINE == "truffleruby"
+
       code = <<~'EOC'
         ①+<<A-②
         #{③*<<B/④