Bump @ember/test-helpers from 2.9.4 to 2.9.6 in /smoke-test-app #1253

Job	Run time
Lint	16s
Tests	30s
Floating Dependencies	27s
Tests (commands smoke test)	0s
format('Smoke Tests (Node v{0} with npm)', matrix.node)	0s
Smoke Tests (Windows)	0s
format('Smoke Tests (Node v{0} with yarn)', matrix.node)	0s
	1m 13s

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