[CALCITE-6749] RelMdUtil#setAggChildKeys may return an incorrect result #14414

Job	Run time
Windows (JDK 17)	13m 58s
Windows (JDK 8)	16m 0s
Linux (JDK 11, Pacific/Chatham Timezone)	10m 17s
Linux (JDK 17)	12m 20s
Linux (JDK 8, latest Guava, America/New_York Timezone)	12m 37s
Linux (JDK 8, oldest Guava, America/New_York Timezone)	10m 59s
Windows (JDK 21)	13m 56s
Linux (JDK 11, Avatica main)	15m 21s
CheckerFramework (JDK 11)	10m 52s
Linux (JDK 21)	10m 12s
Linux (JDK 23)	10m 12s
macOS (JDK 21)	41m 38s
ErrorProne (JDK 11, latest Guava)	4m 8s
CheckerFramework (JDK 11, oldest Guava)	10m 48s
Druid Tests	7m 5s
Linux (JDK 8) Slow Tests	0s
	3h 20m 23s

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