mod: bump cloud.google.com/go/pubsub from 1.47.0 to 1.49.0 #16657

Job	Run time
aux	5m 19s
build	3m 15s
race_dashboard	2m 54s
race	7m 17s
old	6m 50s
dashboard	2m 46s
arch (presubmit_arch_freebsd)	6m 21s
arch (presubmit_arch_netbsd)	3m 52s
gvisor	3m 58s
arch (presubmit_arch_linux)	10m 20s
arch (presubmit_arch_openbsd)	3m 44s
arch (presubmit_arch_windows)	3m 37s
arch (presubmit_arch_darwin)	3m 49s
arch (presubmit_arch_executor)	3m 21s
	1h 7m 23s

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