[ruby/irb] Suppress warning for test which uses a locale non-existing on GitHub Actions

test/irb/test_raise_no_backtrace_exception.rb

@@ -38,6 +38,8 @@ IRB
         end
         env = {}
         %w(LC_MESSAGES LC_ALL LC_CTYPE LANG).each {|n| env[n] = "ja_JP.UTF-8" }
+        # TruffleRuby warns when the locale does not exist
+        env['TRUFFLERUBYOPT'] = "#{ENV['TRUFFLERUBYOPT']} --log.level=SEVERE" if RUBY_ENGINE == 'truffleruby'
         args = [env] + bundle_exec + %W[-rirb -C #{tmpdir} -W0 -e IRB.start(__FILE__) -- -f --]
         error = /`raise_euc_with_invalid_byte_sequence': あ\\xFF \(RuntimeError\)/
         assert_in_out_err(args, <<~IRB, error, [], encoding: "UTF-8")