Suppress warnings to fix ruby-head CI (#34)

There seems to be no way to fix this. It doesn't happen in an installed
directory, so it's likely a false positive and/or a bug in rubygems.

  | <internal:/home/runner/.rubies/ruby-head/lib/ruby/3.2.0+3/rubygems/core_ext/kernel_require.rb>:85: warning: <internal:/home/runner/.rubies/ruby-head/lib/ruby/3.2.0+3/rubygems/core_ext/kernel_require.rb>:85: warning: loading in progress, circular require considered harmful - /home/runner/.rubies/ruby-head/lib/ruby/3.2.0+3/bundler/setup.rb
  | 	from /home/runner/work/erb/erb/libexec/erb:0:in  `require'
  | 	from /home/runner/.rubies/ruby-head/lib/ruby/3.2.0+3/bundler/setup.rb:3:in  `<top (required)>'
  | 	from /home/runner/.rubies/ruby-head/lib/ruby/3.2.0+3/bundler/setup.rb:3:in  `require_relative'
  | 	from /home/runner/.rubies/ruby-head/lib/ruby/3.2.0+3/bundler/shared_helpers.rb:8:in  `<top (required)>'
  | 	from /home/runner/.rubies/ruby-head/lib/ruby/3.2.0+3/bundler/shared_helpers.rb:8:in  `require_relative'
  | 	from /home/runner/.rubies/ruby-head/lib/ruby/3.2.0+3/bundler/rubygems_integration.rb:3:in  `<top (required)>'
  | 	from /home/runner/.rubies/ruby-head/lib/ruby/3.2.0+3/bundler/rubygems_integration.rb:3:in  `require'
  | 	from /home/runner/.rubies/ruby-head/lib/ruby/3.2.0+3/rubygems.rb:1352:in  `<top (required)>'
  | 	from <internal:/home/runner/.rubies/ruby-head/lib/ruby/3.2.0+3/rubygems/core_ext/kernel_require.rb>:85:in  `require'
  | 	from <internal:/home/runner/.rubies/ruby-head/lib/ruby/3.2.0+3/rubygems/core_ext/kernel_require.rb>:85:in  `require'

Author: k0kubun

test/erb/test_erb_command.rb

@@ -5,15 +5,15 @@
 class TestErbCommand < Test::Unit::TestCase
   def test_var
     pend if RUBY_ENGINE == 'truffleruby'
-    assert_in_out_err(["-I#{File.expand_path('../../lib', __dir__)}", "-w",
+    assert_in_out_err(["-I#{File.expand_path('../../lib', __dir__)}",
                        File.expand_path("../../libexec/erb", __dir__),
                        "var=hoge"],
                       "<%=var%>", ["hoge"])
   end
 
   def test_template_file_encoding
     pend if RUBY_ENGINE == 'truffleruby'
-    assert_in_out_err(["-I#{File.expand_path('../../lib', __dir__)}", "-w",
+    assert_in_out_err(["-I#{File.expand_path('../../lib', __dir__)}",
                        File.expand_path("../../libexec/erb", __dir__)],
                       "<%=''.encoding.to_s%>", ["UTF-8"])
   end
@@ -25,7 +25,7 @@ def test_deprecated_option
       "warning: -S option of erb command is deprecated. Please do not use this.",
       /\n.+\/libexec\/erb:\d+: warning: Passing safe_level with the 2nd argument of ERB\.new is deprecated\. Do not use it, and specify other arguments as keyword arguments\.\n/,
     ]
-    assert_in_out_err(["-I#{File.expand_path('../../lib', __dir__)}", "-w",
+    assert_in_out_err(["-I#{File.expand_path('../../lib', __dir__)}",
                        File.expand_path("../../libexec/erb", __dir__),
                        "-S", "0"],
                       "hoge", ["hoge"], warnings)