Wrong value for IOPS allocated on a specific instance

[ligol]

Describe the bug

We currently use the exporter with the associated dashboard and on the exporter directly or on the dashboard I can see the value for rds_max_disk_iops_average of 12000 instead of the 18000 defined actually. We get this issue on the db.r7g.2xlarge but not on the db.r7g.4xlarge

Desktop (please complete the following information)

• OS: Linux
• Prometheus RDS exporter's version 0.10.1
• RDS engine: postgresql

To Reproduce

Deploy a db.r7g.2xlarge with iops defined at 18000