feat(languages): Add Serbian 10k option

[Fooftilly]

Description

I've added a list of 10k words for Serbian, both in Latin and Cyrillic variants.

Checks

• Adding quotes?
  • Make sure to include translations for the quotes in the description (or another comment) so we can verify their content.
• Adding a language or a theme?
  • If is a language, did you edit _list.json, _groups.json and add languages.json?
  • If is a theme, did you add the theme.css?
    • Also please add a screenshot of the theme, it would be extra awesome if you do so!
• Check if any open issues are related to this PR; if so, be sure to tag them below.
• Make sure the PR title follows the Conventional Commits standard. (https://www.conventionalcommits.org for more info)
• Make sure to include your GitHub username inside parentheses at the end of the PR title

[monkeytypegeorge]

Continuous integration check(s) failed. Please review the failing check's logs and make the necessary changes. https://github.com/monkeytypegame/monkeytype/actions/runs/9877363902

[Fooftilly]

I have no idea what I should do about failed check. Please advise.

[fehmer]

Error: Name is not serbian_10k the name property in the json file needs to match the file name.

[monkeytypegeorge]

Continuous integration check(s) failed. Please review the failing check's logs and make the necessary changes. https://github.com/monkeytypegame/monkeytype/actions/runs/9892521471

[Fooftilly]

Updated the names in the new language files. Didn't notice that there is also the language name inside the json files, because I copied and modified original 200 word versions.

[Miodec]

Thanks