app-rails: Update `template-infra:app` to version 0.15.6.post1.dev0+9… #1366

Job	Run time
Lint scripts	5s
Lint GitHub Actions workflows	5s
Validate Terraform modules	1m 6s
Check compliance with tfsec	12s
Check Terraform format	5s
Check compliance with checkov	20s
	1m 53s

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