`make test-bundler-parallel` prints many errors, so try to
downgrade rake version.
```
219) bundle install --standalone run in a subdirectory with --binstubs creates stubs that can be symlinked
Failure/Error:
raise <<~ERROR
#{error_header}
----------------------------------------------------------------------
#{stdboth}
----------------------------------------------------------------------
ERROR
RuntimeError:
Commands:
$ /home/ko1/ruby/build/trunk/ruby -I/home/ko1/ruby/src/trunk/spec/bundler -r/home/ko1/ruby/src/trunk/spec/bundler/support/artifice/compact_index.rb -r/home/ko1/ruby/src/trunk/spec/bundler/support/hax.rb /home/ko1/ruby/src/trunk/tmp/2.13/gems/system/bin/bundle config set --local path /home/ko1/ruby/src/trunk/tmp/2.13/bundled_app/bundle
# $? => 0
Invoking `/home/ko1/ruby/build/trunk/ruby -I/home/ko1/ruby/src/trunk/spec/bundler -r/home/ko1/ruby/src/trunk/spec/bundler/support/artifice/compact_index.rb -r/home/ko1/ruby/src/trunk/spec/bundler/support/hax.rb /home/ko1/ruby/src/trunk/tmp/2.13/gems/system/bin/bundle install --standalone --binstubs` failed with output:
----------------------------------------------------------------------
[DEPRECATED] The --binstubs option will be removed in favor of `bundle binstubs --all`
Could not find compatible versions
Because every version of rails depends on rake = 13.3.0
and rake = 13.3.0 could not be found in rubygems repository https://gem.repo1/ or installed locally,
rails cannot be used.
So, because Gemfile depends on rails >= 0,
version solving has failed.
Fetching gem metadata from https://gem.repo1/...
Resolving dependencies...
----------------------------------------------------------------------
Shared Example Group: "bundle install --standalone" called from ./spec/bundler/install/gems/standalone_spec.rb:532
# /home/ko1/ruby/src/trunk/spec/bundler/support/command_execution.rb:26:in 'Spec::CommandExecution#raise_error!'
# /home/ko1/ruby/src/trunk/spec/bundler/support/subprocess.rb:66:in 'Spec::Subprocess#sh'
# /home/ko1/ruby/src/trunk/spec/bundler/support/helpers.rb:216:in 'Spec::Helpers#sys_exec'
# /home/ko1/ruby/src/trunk/spec/bundler/support/helpers.rb:107:in 'Spec::Helpers#bundle'
# /home/ko1/ruby/src/trunk/spec/bundler/install/gems/standalone_spec.rb:482:in 'block (3 levels) in <top (required)>'
# /home/ko1/ruby/src/trunk/spec/bundler/spec_helper.rb:107:in 'block (4 levels) in <top (required)>'
# /home/ko1/ruby/src/trunk/spec/bundler/spec_helper.rb:107:in 'block (3 levels) in <top (required)>'
# /home/ko1/ruby/src/trunk/spec/bundler/support/helpers.rb:355:in 'block in Spec::Helpers#with_gem_path_as'
# /home/ko1/ruby/src/trunk/spec/bundler/support/helpers.rb:369:in 'Spec::Helpers#without_env_side_effects'
# /home/ko1/ruby/src/trunk/spec/bundler/support/helpers.rb:350:in 'Spec::Helpers#with_gem_path_as'
# /home/ko1/ruby/src/trunk/spec/bundler/spec_helper.rb:106:in 'block (2 levels) in <top (required)>'
```
