Fix double render in project's git URL redirect

What does this MR do?

When you visit the git URL of a project using a browser, we redirect to the project's URL without the git suffix.

When a project is moved, visiting the old URL results in a 500 because we're calling redirect_to twice in the same before_action.

This MR fixes the problem.

https://sentry.gitlab.net/gitlab/gitlabcom/issues/2599907

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

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Security

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