Migrate "app/assets/javascripts/ci/pipeline_editor/components/file_nav/branch_switcher.vue" to GlDisclosureDropdown or GlCollapsibleListbox

One or more dropdowns in app/assets/javascripts/ci/pipeline_editor/components/file_nav/branch_switcher.vue should be migrated to one of the new dropdown components. See the parent epic for guidance on migration strategies.