fix: allow lambda to pass runners roles

[jhatler]

Without this, the lambda fails to launch runners because it does not have the necessary permissions to grant their roles.

Refs: #362

[infracost[bot]]

💰 Infracost report

Monthly estimate generated

Estimate details (includes details of unsupported resources and skipped projects due to errors)

``` ────────────────────────────────── Project: terraform-stacks-runners Module path: terraform/stacks/runners Errors: Failed to lookup module "spacelift.io/jhatler/runner-template/aws" - No versions found for registry module ────────────────────────────────── ────────────────────────────────── 9 projects have no cost estimate changes. Run the following command to see their breakdown: infracost breakdown --path=/path/to/code ────────────────────────────────── 162 cloud resources were detected: ∙ 15 were estimated ∙ 134 were free ∙ 13 are not supported yet, see https://infracost.io/requested-resources: ∙ 10 x aws_network_acl_association ∙ 3 x aws_s3_bucket_lifecycle_configuration ```

_{This comment will be updated when code changes.}