chore(spanner): use channel affinity #20819

Job	Run time
changes	1m 20s
lint	3m 10s
bulk-filter	1m 20s
gapic-libraries-bom	19m 31s
enforcer	15m 18s
generation-config-check	1m 46s
windows	2m 32s
split-units (grpc-gcp-java, 8)	2m 18s
split-dependencies (java-spanner)	3m 35s
split-clirr (java-spanner)	2m 46s
split-units (java-spanner, 8)	4m 38s
split-dependencies (grpc-gcp-java)	2m 11s
split-clirr (grpc-gcp-java)	2m 8s
split-units (java-spanner, 21)	10m 52s
split-units (java-spanner, 25)	6h 0m 53s
split-units (grpc-gcp-java, 21)	2m 20s
split-units (java-spanner, 11)	11m 31s
split-units (grpc-gcp-java, 11)	2m 37s
split-units (java-spanner, 17)	11m 13s
split-units (grpc-gcp-java, 17)	2m 23s
split-units (grpc-gcp-java, 25)	2m 19s
units (8)	59s
units (11)	35s
units (17)	31s
units (25)	32s
units (21)	30s
conditional-required-check	3s
	7h 49m 51s

Provide feedback