Update dependency ember-cli to v6 #1458

Job	Run time
Tests	54s
Floating Dependencies	43s
ember-lts-4.8	41s
ember-lts-3.28	1m 1s
ember-lts-4.12	46s
ember-lts-4.4	42s
embroider-optimized	50s
ember-release-no-deprecations	46s
ember-beta	44s
ember-release	45s
ember-lts-5.12	44s
ember-canary	1m 25s
embroider-safe	1m 6s
ember-modifier-3.2.7	45s
no-deprecations	1m 15s
	13m 7s

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