chore(deps): update dependency @ember/test-helpers to ^2.6.0

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
@ember/test-helpers	`^2.5.0` -> `^2.6.0`

Release Notes

emberjs/ember-test-helpers

### [`v2.6.0`](https://togithub.com/emberjs/ember-test-helpers/blob/master/CHANGELOG.md#v260-2021-11-04) [Compare Source](https://togithub.com/emberjs/ember-test-helpers/compare/v2.5.0...v2.6.0) ##### :rocket: Enhancement - [#1113](https://togithub.com/emberjs/ember-test-helpers/pull/1113) Add `tab` helper (to simulate "tabbing" through focusable elements) ([@NullVoxPopuli](https://togithub.com/NullVoxPopuli)) ##### :bug: Bug Fix - [#1155](https://togithub.com/emberjs/ember-test-helpers/pull/1155) Add registerHooks to new Tab helper ([@NullVoxPopuli](https://togithub.com/NullVoxPopuli)) - [#1141](https://togithub.com/emberjs/ember-test-helpers/pull/1141) Avoid using `Ember.assign` (prevents deprecations on newer Ember versions) ([@ef4](https://togithub.com/ef4)) ##### :house: Internal - [#1149](https://togithub.com/emberjs/ember-test-helpers/pull/1149) Add test confirming lexical scope works with `await render` ([@rwjblue](https://togithub.com/rwjblue)) - [#1153](https://togithub.com/emberjs/ember-test-helpers/pull/1153) Update to ember-source@3.28 in local development ([@rwjblue](https://togithub.com/rwjblue)) - [#1152](https://togithub.com/emberjs/ember-test-helpers/pull/1152) Use latest Embroider version in ember-try config ([@rwjblue](https://togithub.com/rwjblue)) - [#1151](https://togithub.com/emberjs/ember-test-helpers/pull/1151) Add ember-source@3.28 to CI explicitly ([@rwjblue](https://togithub.com/rwjblue)) - [#1150](https://togithub.com/emberjs/ember-test-helpers/pull/1150) Use "normal" script names for `lint:js` ([@rwjblue](https://togithub.com/rwjblue)) ##### Committers: 3 - Edward Faulkner ([@ef4](https://togithub.com/ef4)) - Robert Jackson ([@rwjblue](https://togithub.com/rwjblue)) - [@NullVoxPopuli](https://togithub.com/NullVoxPopuli)