test/irb/test_raise_no_backtrace_exception.rb: fix test file path

Create a file for test under the temporary directory.

test/irb/test_raise_no_backtrace_exception.rb

@@ -29,7 +29,7 @@ IRB
         ENV["HOME"] = tmpdir
 
         bundle_exec = ENV.key?('BUNDLE_GEMFILE') ? ['-rbundler/setup'] : []
-        File.open('euc.rb', 'w') do |f|
+        File.open("#{tmpdir}/euc.rb", 'w') do |f|
           f.write(<<~EOF)
             # encoding: euc-jp
 
@@ -40,7 +40,9 @@ IRB
         end
         env = {}
         %w(LC_MESSAGES LC_ALL LC_CTYPE LANG).each {|n| env[n] = "ja_JP.UTF-8" }
-        assert_in_out_err([env] + bundle_exec + %w[-rirb -W0 -e IRB.start(__FILE__) -- -f --], <<~IRB, /`raise_euc_with_invalid_byte_sequence': あ\\xFF \(RuntimeError\)/, [], encoding: "UTF-8")
+        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")
           require_relative 'euc'
           raise_euc_with_invalid_byte_sequence
         IRB