Skip secret push protection when pushing

The merge-train project is used to sync changes between different projects such as between gitlab-org/gitlab and gitlab-org/security/gitlab.

The changes synced by the merge-train project are always changes that have already been reviewed and merged. Secret push protection should be on when the original commit author pushes their changes to their branch. By the time a commit is being pushed to another project by merge-train, it is already quite late to catch any exposed secrets.

As described in https://gitlab.com/gitlab-com/gl-infra/delivery/-/issues/20491#note_2767931529, merge-train is failing with 500 errors when pushing changes from gitlab-org/gitlab to gitlab-org/security/gitlab. This is blocking deployments.

Related to https://gitlab.com/gitlab-com/gl-infra/delivery/-/issues/20491