mod: bump cloud.google.com/go/spanner from 1.82.0 to 1.87.0 #18646

Job	Run time
dashboard	2m 32s
build	3m 32s
race_dashboard	3m 5s
aux	4m 9s
race	9m 1s
old	7m 10s
gvisor	4m 14s
arch (presubmit_arch_windows)	3m 14s
arch (presubmit_arch_linux)	10m 54s
arch (presubmit_arch_darwin)	3m 47s
arch (presubmit_arch_openbsd)	3m 58s
arch (presubmit_arch_executor)	3m 23s
arch (presubmit_arch_netbsd)	4m 1s
arch (presubmit_arch_freebsd)	6m 26s
	1h 9m 26s

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