Fixing malformed policy bug in oidc roles

[julialawrence]

Pull Request Objective

This piece of work is being tracked in #4358 GitHub Issue.

This is fixing the malformed policy error when no target role is specified in the oidc role config.
Introduced in this PR: #4648

Checklist

Note

Each items should be checked. Skipping below checks could delay your PR review!

• I have reviewed the style guide
  and ensured that my code complies with it
• All checks have passed (or override label applied, if I've
  used the override-static-analysis label, I've explained why)
• I have self-reviewed my code
• I have reviewed the checks and can attest they're as expected

Additional Comments

[github-actions]

Terraform Component 🧱: aws-analytical-platform-oidc

Checkov 🛂: failure

Trivy 🛂: success

Static Analysis Override Label 🏷️: true

Pusher: @julialawrence, Action: pull_request, Working Directory: terraform/aws/analytical-platform/oidc, Workflow: Terraform, Marker: aws-analytical-platform-oidc_static_analysis

[github-actions]

Terraform Component 🧱: aws-analytical-platform-oidc

Terraform Initialization ⚙️: success

Terraform Validation 🤖: success

Terraform Plan 🛠️: success

Pusher: @julialawrence, Action: pull_request, Working Directory: terraform/aws/analytical-platform/oidc, Workflow: Terraform, Marker: aws-analytical-platform-oidc_plan

[Gary-H9]

LGTM