impr(language): add 'buffer' to list of keywords in luau language (adammehaney)

[adammehaney]

Description

Simply adds 'buffer' to the list of Luau keywords as it is specified to exist in the Luau language as a library.

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)
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[Miodec]

Thanks