v3.7.0

Fixed

• TransactionCommitted event was being trigger before the transaction finished. It will now be triggered after the transaction is finished, which will be in align with other database drivers.
• All == was changed to === where it made sense to do so.

Changed

• Use php 7.4 for tests
• Downgrade grpc to 1.35 due to bug in 1.36 (googleapis/google-cloud-php#3911)