Update dependency testdouble to v3.20.1 - autoclosed #2415

Job	Run time
Floating Dependencies	1m 46s
Tests	2m 16s
Try: ember-default-with-jquery	44s
Try: ember-default-with-mocha	31s
Try: ember-classic	28s
Try: embroider-safe	29s
Try: embroider-safe-with-mocha	32s
Try: embroider-optimized	27s
Try: embroider-optimized-with-mocha	28s
Try: ember-lts-3.24	30s
Try: ember-lts-3.20	30s
Try: ember-release	29s
Try: ember-beta	45s
Try: ember-canary	40s
Try: ember-qunit-4	30s
	11m 5s

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