Fix v-on usage of undefined

Vue.js 2 allowed v-on="undefined", while Vue.js 3 expects v-on={} for an empty handler

We need to refactor all undefineds to use {} instead

Offenders:

• ee/app/assets/javascripts/admin/subscriptions/show/components/subscription_activation_card.vue
• ee/app/assets/javascripts/admin/subscriptions/show/components/app.vue
• app/assets/javascripts/ci/runner/components/search_tokens/tag_token.vue