[ruby/irb] Skip the few failing tests on TruffleRuby

https://github.com/ruby/irb/commit/22717844c0

test/irb/test_context.rb

@@ -68,6 +68,7 @@ module TestIRB
     end
 
     def test_evaluate_with_encoding_error_without_lineno
+      skip if RUBY_ENGINE == 'truffleruby'
       assert_raise_with_message(EncodingError, /invalid symbol/) {
         @context.evaluate(%q[{"\xAE": 1}], 1)
         # The backtrace of this invalid encoding hash doesn't contain lineno.
@@ -75,6 +76,7 @@ module TestIRB
     end
 
     def test_evaluate_with_onigmo_warning
+      skip if RUBY_ENGINE == 'truffleruby'
       assert_warning("(irb):1: warning: character class has duplicated range: /[aa]/\n") do
         @context.evaluate('/[aa]/', 1)
       end

test/irb/test_raise_no_backtrace_exception.rb

@@ -4,6 +4,7 @@ require 'test/unit'
 module TestIRB
   class TestRaiseNoBacktraceException < Test::Unit::TestCase
     def test_raise_exception
+      skip if RUBY_ENGINE == 'truffleruby'
       bundle_exec = ENV.key?('BUNDLE_GEMFILE') ? ['-rbundler/setup'] : []
       assert_in_out_err(bundle_exec + %w[-rirb -W0 -e IRB.start(__FILE__) -- -f --], <<-IRB, /Exception: foo/, [])
       e = Exception.new("foo")