[Rerun workflow] update username

[gurevichdmitry]

Summary of your changes

The PR_AUTHOR was initially extracted from github.event.workflow_run.head_commit.author.email, and this field may vary based on individual user configurations, leading to potential inconsistencies. To avoid creating specific logic for each case, it is preferable to use github.actor, which is passed through the GitHub context. This PR replaces the usage of the PR_AUTHOR environment variable with github.actor.

Screenshot/Data

Related Issues

Checklist

• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary README/documentation (if appropriate)

Introducing a new rule?

• Generate rule metadata using this script
• Add relevant unit tests
• Generate relevant rule templates using this script, and open a PR in elastic/packages/cloud_security_posture

[mergify]

This pull request does not have a backport label. Could you fix it @gurevichdmitry? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v./d./d./d is the label to automatically backport to the 8./d branch. /d is the digit
  NOTE: backport-skip has been added to this pull request.