fix: Root instance not found when using with Vue 2.7 (#1379)

* fix: instance root not found

* refactor: const

* style: redundant space

Co-authored-by: Marcel Engelke <marcel.engelke@frederix-hotspot.de>

Author: marcel-engelke

packages/vue-apollo-composable/src/util/loadingTracking.ts

@@ -13,7 +13,7 @@ export interface AppLoadingTracking extends LoadingTracking {
 
 export function getAppTracking () {
   const vm = getCurrentInstance() as CurrentInstance | null
-  const root = vm?.$root ?? vm?.root
+  const root = vm?.$root ?? vm?.root ?? vm?.proxy?.$root as CurrentInstance | null | undefined
   if (!root) {
     throw new Error('Instance $root not found')
   }