Shouldn't TransactionCommitting event be triggered on every transaction level?

[taka-oyama]

I was trying to add TransactionCommitting event (introduced in 9.36.4) to laravel-spanner and noticed that it is only executed when transaction level is at 1 but TransactionBegan and TransactionCommitted event is triggered regardless of transaction level.

Shouldn't TransactionCommitting performed the same as other transaction events?

I wanted to ask before I make a fix PR, since this will be a breaking change and didn't know if it was worth breaking existing code.