Fix typo in vllm extra requirements

[chicham]

Fixes #1314

🚧 Thank you for opening a PR!

A few important guidelines and requirements before we can merge your PR:

• We should be able to understand what the PR does from its title only;
• There is a high-level description of the changes;
• If I add a new feature, there is an issue discussing it already;
• There are links to all the relevant issues, discussions and PRs;
• The branch is rebased on the latest main commit;
• Commit messages follow these guidelines;
• One commit per logical change;
• The code respects the current naming conventions;
• Docstrings follow the numpy style guide;
• pre-commit is installed and configured on your machine, and you ran it before opening the PR;
• There are tests covering the changes;
• The documentation is up-to-date;

Consider opening a Draft PR if your work is still in progress but you would
like some feedback from other contributors.

[rlouf]

Good find, thank you for submitting a fix!