Typo present in enhanced metrics scraper for rds_exporter

Impact on the user
Minimal

Steps to reproduce

• Configure PMM with debug enabled
• Add an RDS instance without enhanced metrics
• Check log

Actual result
Enhanced Metrics are dissabled for instance: <instance>

Expected Result
Enhanced Metrics are disabled for instance: <instance>

Workaround
N/A

Details
There is a typo in the debug message that indicates when an RDS instance does not have enhanced metrics enabled.