Update copy to clipboard icon

Purpose

Updates copy to clipboard icon (full discussion in Update icon - `Copy to clipboard` and deprecate... (#451 - closed))

Screenshots

Before	After

Checklist

For a new icon and/or illustration:

• Link to related design issue: #451 (closed)
• If this adds an icon ensure that it follows the new icon checklists.
• If this adds an illustration ensure that it follows the new illustration checklists.

For third-party trademarks:

• If this adds or updates an icon or illustration that includes a third-party trademark, ensure that it follows the process for adding third-party trademarks to GitLab.
• ✂️ UX Paper Cuts 18.4 → AI (gitlab#548836 - closed)