CI: T7579: fix of the run trigger for CLA

[evgsentrium]

Change Summary

The current implementation of the CLA has an issue when the CLA check workflow fails due to insufficient access to the necessary GA secret. This problem arises from an incorrect run trigger pull_request, which needs to be replaced with the appropriate trigger pull_request_target.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Other (please describe):

Related Task(s)

https://vyos.dev/T7579

Related PR(s)

Proposed changes

How to test

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly