Fix failing CI/CD add/remove variable test

The selector name was wrong, causing the QA smoke test to fali.

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/214910

app/assets/javascripts/ci_variable_list/components/ci_key_field.vue

@@ -132,7 +132,7 @@ export default {
           aria-controls="token-suggestions"
           aria-haspopup="listbox"
           :aria-expanded="showSuggestions"
-          data-qa-selector="variable_key"
+          data-qa-selector="ci_variable_key_field"
           @input="onEntry"
           @keydown.down="onArrowDown"
           @keydown.up="onArrowUp"