Fix dropdown in CI/CD variables not showing the current type

What does this MR do and why?

We were using the wrong constants in the new CI/CD variable dropdown which resulted in the currently selected type not to be shown. This commit now make use of the right constant.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Enable the feature flag

Feature.enable(:ci_variable_settings_graphql)

1. Visit /$user/$Project/-/settings/ci_cd
2. Add a variable
3. Select a type (example, File)
4. Save the variable
5. Click to edit the variable
6. Notice the selected type is shown

MR acceptance checklist

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