Fix the leak in `TestRDocGeneratorDarkfish#test_generated_method_with_html_tag_yield`

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60195 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/rdoc/test_rdoc_generator_darkfish.rb

@@ -215,6 +215,7 @@ class TestRDocGeneratorDarkfish < RDoc::TestCase
     method_name_index = internal_file.index('<span class="method-name">method_with_html_tag_yield</span>')
     last_of_method_name_index = method_name_index + internal_file[method_name_index..-1].index('<div class="method-description">') - 1
     method_name = internal_file[method_name_index..last_of_method_name_index]
+    f.close
 
     assert_includes method_name, '{ |%&lt;&lt;script&gt;alert(&quot;atui&quot;)&lt;/script&gt;&gt;, yield_arg| ... }'
   end