chore: Fix Managed Policy ARNs with hardcoded partition in tests

[samson-keung]

Issue #, if available

None

Description of changes

In some of the integ test templates, for managed policies, it is using an ARN with hardcoded AWS partition. This will fail the test in some regions, hence, replacing the partition part with the AWS::Partition parameter. Example of other places where this is already done.

Description of how you validated changes

Followed the other places in the code where this is already done

Checklist

• Adheres to the development guidelines
• [n/a] Add/update transform tests
  • Using correct values
  • Using wrong values
• Add/update integration tests

Examples?

Please reach out in the comments if you want to add an example. Examples will be
added to sam init through aws/aws-sam-cli-app-templates.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.