Update twitter logo (#9303)

_Description of what this PR is changing or adding, and why:_

This PR updates the old Twitter logo to the new one, ensuring the
website remains up to date.

_Issues fixed by this PR (if any):_

This PR doesn't address a specific issue directly.

## Presubmit checklist

- [x] This PR doesn’t contain automatically generated corrections
(Grammarly or similar).
- [x] This PR follows the [Google Developer Documentation Style
Guidelines](https://developers.google.com/style) — for example, it
doesn’t use _i.e._ or _e.g._, and it avoids _I_ and _we_ (first person).
- [x] This PR uses [semantic line
breaks](https:/dart-lang/site-shared/blob/main/doc/writing-for-dart-and-flutter-websites.md#semantic-line-breaks)
of 80 characters or fewer.

Co-authored-by: Anthony Sansone <[email protected]>