17.2 backport for fix PEP when SEC is available

What does this MR do and why?

Backport !159845 (merged) to 17.2

Fix Pipeline execution policy error: job names must be unique error by ignoring scan execution policies when pipeline execution policy is available.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
• The MR that fixed the bug on the default branch has been deployed to GitLab.com (not applicable for documentation or spec changes).
• This MR has a severity label assigned (if applicable).
• Set the milestone of the merge request to match the target backport branch version.
• This MR has been approved by a maintainer (only one approval is required).
• Ensure the e2e:package-and-test-ee job has either succeeded or been approved by a Software Engineer in Test.

Note to the merge request author and maintainer

If you have questions about the patch release process, please:

• Refer to the patch release runbook for engineers and maintainers for guidance.
• Ask questions on the #releases Slack channel (internal only).

Screenshots or screen recordings

Before

How to set up and validate locally

1. Create a scan execution policy enforcing a security scan such as SAST.
2. Create a pipeline execution policy creating any job, such as basic job with an echo script.
3. Create a project for that the policies apply with a .gitlab-ci.yml file.
4. Verify that pipeline starts and there's no failure in given projects.

See example group: https://gitlab.com/gitlab-org/govern/security-policies/andys-test-group/reproduce-issue-473112

Related issue: #473112 (closed)