Flaky test with macOS platform

I sometimes got the following failure with ruby/ruby and make test-bundled-gems.

Testing the net-imap gem
/Users/hsbt/Documents/github.com/ruby/ruby/exe/ruby -C /Users/hsbt/Documents/github.com/ruby/ruby/gems/src/net-imap /Users/hsbt/Documents/github.com/ruby/ruby/.bundle/bin/rake test
Loaded suite /Users/hsbt/Documents/github.com/ruby/ruby/.bundle/gems/rake-13.2.1/lib/rake/rake_test_loader
Started
/Users/hsbt/Documents/github.com/ruby/ruby/.bundle/gems/test-unit-3.6.2/lib/test/unit/fixture.rb:284: warning: the block passed to 'priority_setup' defined at /Users/hsbt/Documents/github.com/ruby/ruby/.bundle/gems/test-unit-3.6.2/lib/test/unit/priority.rb:183 may be ignored
F
====================================================================================================================================================================================
Failure: test_imaps_with_ca_file(IMAPTest):
  Exception raised:
  <#<OpenSSL::SSL::SSLError: SSL_read: tlsv1 alert unknown ca (SSL alert number 48)>>
  Backtrace:
    /Users/hsbt/Documents/github.com/ruby/ruby/.ext/common/openssl/buffering.rb:80:in 'OpenSSL::SSL::SSLSocket#sysread'
    /Users/hsbt/Documents/github.com/ruby/ruby/.ext/common/openssl/buffering.rb:80:in 'OpenSSL::Buffering#fill_rbuff'
    /Users/hsbt/Documents/github.com/ruby/ruby/.ext/common/openssl/buffering.rb:236:in 'OpenSSL::Buffering#gets'
    /Users/hsbt/Documents/github.com/ruby/ruby/gems/src/net-imap/lib/net/imap.rb:2720:in 'Net::IMAP#get_response'
    /Users/hsbt/Documents/github.com/ruby/ruby/gems/src/net-imap/lib/net/imap.rb:2629:in 'Net::IMAP#receive_responses'
    /Users/hsbt/Documents/github.com/ruby/ruby/gems/src/net-imap/lib/net/imap.rb:2606:in 'block in Net::IMAP#start_receiver_thread'.
/Users/hsbt/Documents/github.com/ruby/ruby/.ext/common/openssl/buffering.rb:80:in 'OpenSSL::SSL::SSLSocket#sysread'
/Users/hsbt/Documents/github.com/ruby/ruby/.ext/common/openssl/buffering.rb:80:in 'OpenSSL::Buffering#fill_rbuff'
/Users/hsbt/Documents/github.com/ruby/ruby/.ext/common/openssl/buffering.rb:236:in 'OpenSSL::Buffering#gets'
/Users/hsbt/Documents/github.com/ruby/ruby/gems/src/net-imap/lib/net/imap.rb:2720:in 'Net::IMAP#get_response'
/Users/hsbt/Documents/github.com/ruby/ruby/gems/src/net-imap/lib/net/imap.rb:2629:in 'Net::IMAP#receive_responses'
/Users/hsbt/Documents/github.com/ruby/ruby/gems/src/net-imap/lib/net/imap.rb:2606:in 'block in Net::IMAP#start_receiver_thread'
====================================================================================================================================================================================
Finished in 8.730846 seconds.
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
818 tests, 8689 assertions, 1 failures, 0 errors, 0 pendings, 0 omissions, 0 notifications
99.8778% passed
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
93.69 tests/s, 995.21 assertions/s
rake aborted!
Command failed with status (1)
/Users/hsbt/Documents/github.com/ruby/ruby/.bundle/gems/rake-13.2.1/exe/rake:27:in '<top (required)>'
Tasks: TOP => test
(See full trace by running task with --trace)
Tests failed with exit code 1

My environment is macOS 14.5 with Apple Silicon and using OpenSSL 3 library provided from homebrew.

Start by reproducing the failure with make test-bundled-gems in the net-imap tests, focusing on test_imaps_with_ca_file(IMAPTest) and the reported macOS 14.5/OpenSSL 3 environment. Trace the CA-related TLS setup and test timing; done means the test no longer flakes on that platform while still verifying the intended CA-file behavior.