fix(test): ensure `includeNullModifier` value is honored

[dancormier]

After having visual failures of test(select): add a11y, visual tests #1498 after it had been updated with the latest test changes in develop, I realized something was not working as expected.

Turns out that we're not fully honoring the includeNullModifier option for secondary and global modifiers (this bug predates the recent test changes). This PR fixes that bug.

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