This resolves an "ArgumentError: comparison of String with 0 failed"
issue where the visibility_level is stored as a string in the project
import data because the value comes directly from the Web form. This
problem happened upon creating a project from a template or restoring a
project.

We now cast the value to an integer to guard against these kinds of
failures.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/61692