upgrade ember-qunit integration per Ember CLI v6.2 blueprints #1469

Job	Run time
Tests	1m 14s
Floating Dependencies	58s
ember-lts-3.28	45s
ember-lts-4.4	1m 0s
ember-release	43s
ember-lts-4.12	41s
ember-beta	49s
ember-lts-4.8	46s
no-deprecations	55s
ember-canary	1m 2s
ember-lts-5.12	46s
embroider-safe	1m 9s
ember-modifier-3.2.7	44s
embroider-optimized	49s
ember-release-no-deprecations	51s
	13m 12s

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