Fix automerge workflow for external users and bots

[lfilho]

Problem

Out automerge workflow checks for our ops-bot user in order to kick in and auto merge our release auto-cut PRs.

We're using a repo-scoped PAT (Personal Access Token). This mean that the github.actor in our github action will be whichever user generated that token (lfilho in this case).

See https://github.com/peter-evans/create-pull-request/blob/master/docs/concepts-guidelines.md#triggering-further-workflow-runs for more details.

Solution

We probably want to do https://github.com/peter-evans/create-pull-request/blob/master/docs/concepts-guidelines.md#push-pull-request-branches-to-a-fork as it's the most secure approach.

Temporary workaround

As I'm the only developer here so far, I have just changed the check to accept my username and instead I'm adding another condition to check for the specific automerge label.