tools: temporarily unset LD_LIBRARY_PATH when generating ssh key #19084

Job	Run time
old	7m 0s
dashboard	2m 10s
race_dashboard	3m 2s
race	6m 8s
build	3m 15s
aux	3m 56s
gvisor	4m 6s
arch (presubmit_arch_openbsd)	3m 21s
arch (presubmit_arch_freebsd)	6m 24s
arch (presubmit_arch_darwin)	3m 44s
arch (presubmit_arch_executor)	3m 19s
arch (presubmit_arch_netbsd)	4m 1s
arch (presubmit_arch_windows)	3m 36s
arch (presubmit_arch_linux)	8m 19s
	1h 2m 21s

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