Disable secret historic scans

From https://docs.gitlab.com/ee/user/application_security/secret_detection/#full-history-secret-detection

You should do a full history scan only once, after enabling Secret Detection. A full history can take a long time, especially for larger repositories with lengthy Git histories. After completing an initial full history scan, use only standard Secret Detection as part of your pipeline.

This MR disables historic scans for secret detection in every pipeline.

closes https://gitlab.com/gitlab-com/gl-security/engineering-and-research/inventory/-/issues/1043