Avoid evaluating it unless/until itAsync called. (#6719)

A safer way to solve #6576 (comment),
given that 4589606 had to be reverted.

This change makes it safe to import the `@apollo/client/testing`
entry point in environments that don't define `global.it`.

src/utilities/testing/itAsync.ts

@@ -1,27 +1,25 @@
-function wrap<TResult>(
-  original: (...args: any[]) => TResult,
-) {
+function wrap<TResult>(key?: "only" | "skip" | "todo") {
   return (
     message: string,
     callback: (
       resolve: (result?: any) => void,
       reject: (reason?: any) => void,
     ) => any,
     timeout?: number,
-  ) => original(message, function () {
+  ) => (key ? it[key] : it)(message, function () {
     return new Promise(
       (resolve, reject) => callback.call(this, resolve, reject),
     );
   }, timeout);
 }
 
-const wrappedIt = wrap(it);
+const wrappedIt = wrap();
 export function itAsync(...args: Parameters<typeof wrappedIt>) {
   return wrappedIt.apply(this, args);
 }
 
 export namespace itAsync {
-  export const only = wrap(it.only);
-  export const skip = wrap(it.skip);
-  export const todo = wrap(it.todo);
+  export const only = wrap("only");
+  export const skip = wrap("skip");
+  export const todo = wrap("todo");
 }