fix(CopyButton): removes additional fill on click animation

[jnm2377]

Closes #11410

Changelog

• Removes border that was getting added on pseudo element for animation on click

Testing / Reviewing

• Go to CopyButton story
  • switch to darker themes (to be able to see the fill easier, even though it exists on all themes)
  • click the copy button
  • animation should work without the additional fill in the icon
• Test out the same way for CodeSnippet multi + single stories

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