fix(select): apply text color to focussed select for firefox

[jendowns]

Closes #4241

It looks like Firefox expects there to be a color set on the select:focus 😲
This style rule appears to fix the issue identified in #4241

Changelog

Changed

• set color: $text-01 when select is focussed

Testing / Reviewing

• open the carbon-components-react deployment in Firefox: https://deploy-preview-4343--the-carbon-components.netlify.com
• set the theme to a dark theme like g100
• select options in the Select component and see that the select option text color stays white (and readable)

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[asudoh]

LGTM 👍 - Thanks @jendowns!

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