Reset environments list when opening CI variable drawer

What does this MR do and why?

Resolves #428429 (closed).

There is a bug in the environment scope dropdown

This is an existing bug that also occurs in the CI variable modal, but since we're phasing the modal out for the drawer and this bug can be , I think we can just focus on fixing the bug on the drawer.

Screenshots or screen recordings

Before	After
Screen_Recording_2023-10-17_at_15.56.10	Screen_Recording_2023-10-17_at_16.08.28

How to set up and validate locally

1. Go to Settings > CI/CD > Variables.
2. Add a CI variable.
3. In the environment scope dropdown, enter an environment that doesn't exist yet. This will cause a search request which returns an empty result.
4. Close the form and re-open it.
5. The environment scope dropdown should reset the environments list to the default (it should not be empty).

MR acceptance checklist

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