Dedupe qualified name for `GroupByMetricSpecs` #3023

Job	Run time
MetricFlow Tests (DuckDB) (3.8)	3m 47s
MetricFlow Tests (PostgreSQL)	2m 56s
MetricFlow Tests (DuckDB) (3.11)	2m 57s
MetricFlow Packages Tests (3.8)	39s
MetricFlow Packages Tests (3.11)	40s
MetricFlow Unit Tests	1s
	11m 0s

Provide feedback