Change the workhorse tools version to 1.19.7

What does this MR do and why?

Updates the golang version used in workhorse development to 1.19.7, which is already part of gdk https://gitlab.com/gitlab-org/gitlab-development-kit/-/blob/main/.tool-versions#L6-26

Workhorse has been testing with 1.19 in CI since !99090 (merged)

Part of &9495 (closed)

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