Fix `Leaked tempfile`s

http://rubyci.s3.amazonaws.com/debian10/ruby-master/log/20200930T033004Z.diff.html.gz
```
 [n/n] JSONCommonInterfaceTest#test_load = <elapsed> s
 [n/n] JSONCommonInterfaceTest#test_load_file = <elapsed> s
+Leaked tempfile: JSONCommonInterfaceTest#test_load_file: #<Tempfile:<build-dir>/tmp/20200930-7601-ptnv6i (closed)>
 [n/n] JSONCommonInterfaceTest#test_load_file! = <elapsed> s
+Leaked tempfile: JSONCommonInterfaceTest#test_load_file!: #<Tempfile:<build-dir>/tmp/20200930-7601-1la6m9 (closed)>
 [n/n] JSONCommonInterfaceTest#test_load_file_with_option = <elapsed> s
+Leaked tempfile: JSONCommonInterfaceTest#test_load_file_with_option: #<Tempfile:<build-dir>/tmp/20200930-7601-blf9hz (closed)>
 [n/n] JSONCommonInterfaceTest#test_load_file_with_option! = <elapsed> s
+Leaked tempfile: JSONCommonInterfaceTest#test_load_file_with_option!: #<Tempfile:<build-dir>/tmp/20200930-7601-b5gsdb (closed)>
```

test/json/json_common_interface_test.rb

@@ -157,27 +157,15 @@ class JSONCommonInterfaceTest < Test::Unit::TestCase
     end
   end
 
-  # Copied and slightly modified from https://github.com/keithrbennett/trick_bag
-  # (https://github.com/keithrbennett/trick_bag/blob/master/lib/trick_bag/io/temp_files.rb).
-  #
-  # For the easy creation and deletion of a temp file populated with text,
-  # wrapped around the code block you provide.
-  #
-  # @param text the text to write to the temporary file
-  # @param file_prefix optional prefix for the temporary file's name
-  # @yield filespec of the temporary file
   def temp_file_containing(text, file_prefix = '')
     raise "This method must be called with a code block." unless block_given?
 
-    filespec = nil
     begin
-      Tempfile.open(file_prefix) do |file|
+      Tempfile.create(file_prefix) do |file|
         file << text
-        filespec = file.path
+        file.close
+        yield file.path
       end
-      yield(filespec)
-    ensure
-      File.delete(filespec) if filespec && File.exist?(filespec)
     end
   end
 end