Before #39304 was merged, backtraces would look like this:
```
$ be ruby -I lib:test test/controller/request_forgery_protection_test.rb -n test_ignores_trailing_slash_during_generation
Run options: -n test_ignores_trailing_slash_during_generation --seed 22205
E
Error:
PerFormTokensControllerTest#test_ignores_trailing_slash_during_generation:
NoMethodError: undefined method `have_cookie_jar?' for #<Object:0x00007f9ce19b9620>
/Users/aaron/git/rails/actionpack/lib/action_controller/test_case.rb:522:in `ensure in process'
/Users/aaron/git/rails/actionpack/lib/action_controller/test_case.rb:542:in `process'
/Users/aaron/git/rails/actionpack/lib/action_controller/test_case.rb:395:in `get'
test/controller/request_forgery_protection_test.rb:1005:in `test_ignores_trailing_slash_during_generation'
rails test test/controller/request_forgery_protection_test.rb:1004
Finished in 0.213230s, 4.6898 runs/s, 0.0000 assertions/s.
1 runs, 0 assertions, 0 failures, 1 errors, 0 skips
```
After #39304 was merged they look like this:
```
$ be ruby -I lib:test test/controller/request_forgery_protection_test.rb -n test_ignores_trailing_slash_during_generation
Run options: -n test_ignores_trailing_slash_during_generation --seed 62892
E
Error:
PerFormTokensControllerTest#test_ignores_trailing_slash_during_generation:
NoMethodError: undefined method `have_cookie_jar?' for #<Object:0x00007fa6d60193c8>
rails test test/controller/request_forgery_protection_test.rb:1004
Finished in 0.211953s, 4.7180 runs/s, 0.0000 assertions/s.
1 runs, 0 assertions, 0 failures, 1 errors, 0 skips
```
This patch reverts the part of #39304 that removes the backtrace.
43ed3c7939