Fix adding extra characters for pipeline execution policy

What does this MR do and why?

This MR fixes adding extra characters

Extra characters were added when yaml is parsed for scan execution policy for ci/cd action

MR acceptance checklist

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Screenshots or screen recordings

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Description	Video
Editing yaml in editor and loading from file	Loom video

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Enable feature flag

Feature.enable(:compliance_pipeline_in_policies)

1. Create a group

2. Go to Settings -> General

3. Toggle the Permissions and group features section

4. Enable Run customized CI YAML file as security policy actions

5. Go to Secure -> Policies

6. Select New policy

7. Select Scan execution policy

8. Select Add new action

9. Select Run CI/CD code

10. Past the following code:

        test job:
            stage: test

11. Observe that the YAML section on the right side contains:

    ci_configuration: |
      |-
        test job:
            stage: test

The correct YAML would be:

ci_configuration: |-
    test job:
        stage: test

12. Create yaml file locally with same content
13. Use load from file option and load content from created file

Related to #439346 (closed)