Update CSS selector name in test helper #994

Job	Run time
Lint (docs-app)	28s
Lint (packages/ember-container-query)	19s
Test (packages/ember-container-query)	21s
Lint (test-app)	26s
Test compatibility (ember-lts-4.4)	46s
Test (test-app)	36s
Build (docs-app)	40s
Test compatibility (ember-lts-4.8)	55s
Test compatibility (ember-lts-4.12)	48s
Test compatibility (ember-lts-5.4)	58s
Test compatibility (ember-lts-5.8)	47s
Test compatibility (ember-release)	59s
Test compatibility (ember-beta)	45s
Test compatibility (ember-canary)	1m 2s
Test compatibility (embroider-safe)	51s
Test compatibility (embroider-optimized)	51s
Test (docs-app) (w1-h1)	1m 7s
Test (docs-app) (w2-h1)	44s
Test (docs-app) (w3-h1)	55s
Test (docs-app) (w1-h2)	44s
Test (docs-app) (w2-h2)	45s
Test (docs-app) (w3-h2)	51s
Test (docs-app) (w1-h3)	55s
Test (docs-app) (w2-h3)	1m 0s
Test (docs-app) (w3-h3)	46s
	19m 19s

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