Fix LanguageNegotiationMethodInterface::getLangcode() result docblock

For the CI failure.

Fixed failed commands on #23
Attached patch against Drupal 10.1.x

@pooja saraah :
Addendum: Read the issue and submitted patch again, no problems there, still
gonna hide the patch file to avoid confusion, feel free to inform me if I am missing something important.

Setting this back to "Needs review" and I believe this is now ready for moving forward.

This issue is being reviewed by the kind folks in Slack, #needs-review-queue-initiative. We are working to keep the size of Needs Review queue [2700+ issues] to around 400 (1 month or less), following Review a patch or merge request → as a guide.

Read the changes to the documentation in MR 3171 and the change make sense and the todo pointing to the issue where it could be fixed helped.
Looks good to me.

Looks good now, thanks!

As a code documentation improvement, this is eligible for backport. So, I committed it to 10.1.x, and cherry-picked it to 10.0.x and 9.5.x. Thanks!

Automatically closed - issue fixed for 2 weeks with no activity.