Update the location dropdown on the Group Dependency List page to use the new GraphQL query (`dependencyLocations`) instead of the existing REST endpoint. This is gated behind the `group_dependency_graphql` feature flag. The BE GraphQL endpoint is introduced in !237674. This issue covers the FE work to wire up the dropdown to consume that query. The UI/UX remains unchanged. Part of &17254 (Migrate dependency filtering to GraphQL: Group-level).