test(bigquery): warm up client in beforeClass to stabilize testFastSQLQueryMultiPage #21721

Job	Run time
bulk-filter	1m 10s
gapic-libraries-bom	19m 26s
changes	31s
windows	2m 15s
units (8)	54s
units (11)	31s
generation-config-check	1m 8s
units (21)	35s
units (17)	43s
units (25)	34s
lint	3m 12s
units (26)	40s
enforcer	20m 12s
split-clirr (java-bigquery)	3m 6s
split-units (java-bigquery, 8)	3m 37s
split-units (java-bigquery, 11)	3m 58s
split-units (java-bigquery, 21)	3m 12s
split-dependencies (java-bigquery)	3m 17s
split-units (java-bigquery, 25)	3m 46s
split-units (java-bigquery, 17)	3m 48s
split-units (java-bigquery, 26)	3m 45s
conditional-required-check	3s
	1h 20m 23s

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