style: Do not use tabs

Most Typescript projects at GitLab do not use tabs:

• https://gitlab.com/gitlab-org/gitlab-web-ide/-/blob/main/.prettierrc?ref_type=heads
• https://gitlab.com/gitlab-org/gitlab-vscode-extension/-/blob/main/.prettierrc?ref_type=heads
• https://gitlab.com/gitlab-org/editor-extensions/gitlab-lsp/-/blob/main/.prettierrc.json?ref_type=heads

The default for useTabs is false (https://prettier.io/docs/en/options#tabs)