use pnpm #409

Job	Run time
Floating Dependencies	1m 2s
Tests	3m 6s
Percy Tests	3m 6s
ember-canary - Allowed to fail	1m 30s
ember-lts-3.28	1m 37s
ember-release-no-deprecations - Allowed to fail	1m 42s
ember-release	1m 13s
ember-beta	1m 4s
ember-classic	1m 42s
ember-default-with-jquery	1m 3s
embroider-safe	1m 32s
embroider-optimized	1m 20s
no-deprecations	1m 32s
	21m 29s

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