Fix some flaky test failures on Windows

[deivid-rodriguez]

What was the end-user or developer problem that led to this PR?

There's a longstanding flaky CI failure on Windows that reads like this:

4 processes for 172 specs, ~ 43 specs per process

Randomized with seed 26551


An error occurred in a `before(:suite)` hook.
Failure/Error: FileUtils.cp shipped_file, target_shipped_file, preserve: true

Errno::EACCES:
  Permission denied - read
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/lib/ruby/3.3.0/fileutils.rb:2280:in `copy_stream'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/lib/ruby/3.3.0/fileutils.rb:2280:in `block (2 levels) in copy_file'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/lib/ruby/3.3.0/fileutils.rb:2279:in `open'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/lib/ruby/3.3.0/fileutils.rb:2279:in `block in copy_file'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/lib/ruby/3.3.0/fileutils.rb:2278:in `open'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/lib/ruby/3.3.0/fileutils.rb:2278:in `copy_file'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/lib/ruby/3.3.0/fileutils.rb:1078:in `copy_file'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/lib/ruby/3.3.0/fileutils.rb:877:in `block in cp'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/lib/ruby/3.3.0/fileutils.rb:2469:in `block in fu_each_src_dest'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/lib/ruby/3.3.0/fileutils.rb:2485:in `fu_each_src_dest0'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/lib/ruby/3.3.0/fileutils.rb:2467:in `fu_each_src_dest'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/lib/ruby/3.3.0/fileutils.rb:876:in `cp'
# ./spec/support/builders.rb:432:in `block in _build'
# ./spec/support/builders.rb:426:in `each'
# ./spec/support/builders.rb:426:in `_build'
# ./spec/support/helpers.rb:280:in `with_built_bundler'
# ./spec/support/helpers.rb:260:in `block (2 levels) in system_gems'
# ./spec/support/helpers.rb:256:in `each'
# ./spec/support/helpers.rb:256:in `block in system_gems'
# ./spec/support/helpers.rb:289:in `block in with_gem_path_as'
# ./spec/support/helpers.rb:303:in `without_env_side_effects'
# ./spec/support/helpers.rb:284:in `with_gem_path_as'
# ./spec/support/helpers.rb:254:in `system_gems'
# ./spec/spec_helper.rb:91:in `block (2 levels) in <top (required)>'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/lib/ruby/gems/3.3.0/gems/rspec-core-3.13.0/lib/rspec/core/example.rb:457:in `instance_exec'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/lib/ruby/gems/3.3.0/gems/rspec-core-3.13.0/lib/rspec/core/example.rb:457:in `instance_exec'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/lib/ruby/gems/3.3.0/gems/rspec-core-3.13.0/lib/rspec/core/hooks.rb:365:in `run'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/lib/ruby/gems/3.3.0/gems/rspec-core-3.13.0/lib/rspec/core/configuration.rb:2185:in `block in run_suite_hooks'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/lib/ruby/gems/3.3.0/gems/rspec-core-3.13.0/lib/rspec/core/configuration.rb:2183:in `each'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/lib/ruby/gems/3.3.0/gems/rspec-core-3.13.0/lib/rspec/core/configuration.rb:2183:in `run_suite_hooks'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/lib/ruby/gems/3.3.0/gems/rspec-core-3.13.0/lib/rspec/core/configuration.rb:2090:in `with_suite_hooks'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/lib/ruby/gems/3.3.0/gems/rspec-core-3.13.0/lib/rspec/core/runner.rb:116:in `block in run_specs'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/lib/ruby/gems/3.3.0/gems/rspec-core-3.13.0/lib/rspec/core/reporter.rb:74:in `report'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/lib/ruby/gems/3.3.0/gems/rspec-core-3.13.0/lib/rspec/core/runner.rb:115:in `run_specs'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/lib/ruby/gems/3.3.0/gems/rspec-core-3.13.0/lib/rspec/core/runner.rb:89:in `run'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/lib/ruby/gems/3.3.0/gems/rspec-core-3.13.0/lib/rspec/core/runner.rb:71:in `run'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/lib/ruby/gems/3.3.0/gems/rspec-core-3.13.0/lib/rspec/core/runner.rb:45:in `invoke'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/lib/ruby/gems/3.3.0/gems/rspec-core-3.13.0/exe/rspec:4:in `<top (required)>'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/bin/rspec:25:in `load'
# C:/hostedtoolcache/windows/Ruby/3.3.1/x64/bin/rspec:25:in `<main>'
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See for example https://github.com/rubygems/rubygems/actions/runs/9663003543/job/26654152938.

What is your fix for the problem, implemented in this PR?

My diagnosis is that when starting the parallelized test suite, multiple processes copy source files necessary to build bundler to its own folder in tmp/. On Windows, this can apparently result in permission errors, I guess because the file is in use by another process.

As a workaround, I changed building bundler in CI to happen just once at bin/rake spec:deps time, not on the fly when running specs.

I expect this to make this error not happen again.

Make sure the following tasks are checked

• Describe the problem / feature
• Write tests for features and bug fixes
• Write code to solve the problem
• Make sure you follow the current code style and write meaningful commit messages without tags