Bump follow-redirects from 1.14.9 to 1.15.6 in /terraform/environments/xhibit-portal/scripts/perf #2471

Job	Run time
destroy-development	0s
strategy / strategy	2s
terraform (preproduction, plan) / plan	2m 23s
terraform (development, plan_apply) / plan	2m 30s
terraform (production, plan) / plan	1m 22s
terraform (production, plan) / apply	0s
terraform (preproduction, plan) / apply	0s
terraform (development, plan_apply) / apply	0s
	6m 17s

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