Support in-flight jobs stored before individual execution counters for `retry_on` (#34731)

Also, make tests and examples for individual execution counters
clearer, as it wasn't entierly clear what would happen in this case:

```
retry_on CustomException, OtherException, attempts: 3
```

The job would be retried at most 3 times in total, for both
CustomException and OtherException. To have the job retry 3 times at
most for each exception individually, the following retry_on
declarations are necessary:

```
retry_on CustomException, attempts: 3
retry_on OtherException, attempts: 3
```

1 files changed, 3 insertions, 11 deletions

diff --git a/activejob/test/jobs/retry_job.rb b/activejob/test/jobs/retry_job.rb
index 2d19d4c41e..3b0dce1a3c 100644
--- a/activejob/test/jobs/retry_job.rb
+++ b/activejob/test/jobs/retry_job.rb
@@ -18,7 +18,7 @@ class CustomDiscardableError < StandardError; end
 
 class RetryJob < ActiveJob::Base
   retry_on DefaultsError
-  retry_on FirstRetryableErrorOfTwo, SecondRetryableErrorOfTwo
+  retry_on FirstRetryableErrorOfTwo, SecondRetryableErrorOfTwo, attempts: 4
   retry_on LongWaitError, wait: 1.hour, attempts: 10
   retry_on ShortWaitTenAttemptsError, wait: 1.second, attempts: 10
   retry_on ExponentialWaitTenAttemptsError, wait: :exponentially_longer, attempts: 10
@@ -31,7 +31,8 @@ class RetryJob < ActiveJob::Base
   discard_on(CustomDiscardableError) { |job, error| JobBuffer.add("Dealt with a job that was discarded in a custom way. Message: #{error.message}") }
 
   def perform(raising, attempts)
-    if executions < attempts
+    raising = raising.shift if raising.is_a?(Array)
+    if raising && executions < attempts
       JobBuffer.add("Raised #{raising} for the #{executions.ordinalize} time")
       raise raising.constantize
     else
@@ -39,12 +40,3 @@ class RetryJob < ActiveJob::Base
     end
   end
 end
-
-class ExceptionRetryJob < ActiveJob::Base
-  retry_on FirstRetryableErrorOfTwo, SecondRetryableErrorOfTwo, attempts: 4
-  retry_on DefaultsError
-
-  def perform(exceptions)
-    raise exceptions.shift.constantize.new unless exceptions.empty?
-  end
-end