[CALCITE-6137] Upgrade Gradle from 8.1.1 to 8.5, support jdk21 #564

Job	Run time
Linux (JDK 11), Middle-Aged Guava	4m 1s
Linux (JDK 11), Newest Guava	4m 17s
Linux (JDK 11), Calcite Minimum Guava, America/New_York Timezone	3m 56s
Linux (JDK 11), Oldest Guava, Pacific/Chatham Timezone	4m 6s
Linux (JDK 17)	4m 7s
Linux (JDK 21)	3m 48s
Linux (JDK 8)	3m 56s
Linux (JDK 8), Avatica main	12m 38s
macOS (JDK 21)	9m 16s
Windows (JDK 11)	5m 5s
	55m 10s

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