Add GHA_Actor parameter to allow user's override

[szobov]

Hello, dear maintainers,

I ran into the issue when my CircleCI's job was triggered from the PR created by dependabot but failed because dependabot is not known to CircleCI. When the same job is triggered with GHA_Actor, an existing user, it passes.

To overcome this issue, I added GHA_Actor as a parameter so that users could override it if needed.

I didn't touch documentation much, but I am open to any suggestions. Thanks a lot for your time and support!