[ruby/rubygems] Do not create unnecessary directories

The method `Spec::Path#vendored_gems` creates the directory containing
the path.  It makes no sense to create a directory with the same name
as its basename in the current working directory.

ruby/rubygems@725f4ff2f4

Author: nobu

spec/bundler/commands/clean_spec.rb

@@ -913,12 +913,10 @@ def should_not_have_gems(*gems)
     # Simulate that the locked bundler version is installed in the bundle path
     # by creating the gem directory and gemspec (as would happen after bundle install with that version)
     Pathname(vendored_gems("cache/bundler-#{version}.gem")).tap do |path|
-      path.basename.mkpath
       FileUtils.touch(path)
     end
     FileUtils.touch(vendored_gems("gems/bundler-#{version}"))
     Pathname(vendored_gems("specifications/bundler-#{version}.gemspec")).tap do |path|
-      path.basename.mkpath
       path.write(<<~GEMSPEC)
         Gem::Specification.new do |s|
           s.name = "bundler"