Send environment to render validation error instead of deployment (nil)

What does this MR do and why?

This fixes a bug in the deployment API, if you enter an invalid environment name, it will hang at render_validation_error!, which we give the variable deployment. deployment does not exist until a few lines later. We also want to fail this on environment errors. As an added bonus this will improve spec performance of ./spec/requests/api/deployments_spec.rb:192 by 5+ minutes

How to set up and validate locally

1. Do an API call with an invalid environment name: curl --header "PRIVATE-TOKEN: <private token>" -X POST --data "environment=aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa&sha=f15b32277d2c55c6c595845a87109b09c913c556&ref=master&tag=false&status=success" "http://gdk.test:3000/api/v4/projects/6/deployments". On the old code it will timeout after 5 minutes and send a 500 Internal Server Error. On the new code it will fail fast and still send a 500 error (with an error message explaining why it fails)

MR acceptance checklist

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Related to #382547 (closed)