fix(form-field): proper arrow color for native select

[crisbeto]

Fixes the arrow color for a focused native select that is projected inside a mat-form-field.

[ngbot]

I see that you just added the pr: merge ready label, but the following checks are still failing:
     status "ci/circleci: tests_saucelabs" is failing
     status "ci/circleci: tests_browserstack" is pending

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