Add `--exclude-tests` to support two-phased migration #353

Job	Run time
Install	21s
Types: Tests	37s
Test: base-js-v1-addon	6m 14s
Test: base-ts-v1-addon	6m 29s
Test: ember-autofocus-modifier-v5.0.0	3m 23s
Types: Library	21s
Lint JS	29s
Release	0s
	17m 54s

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