Handle special characters in RepositoryService

Followup from MR: gitlab-org/editor-extensions/gitlab-lsp!800 (diffs, comment 2111933480)

// TODO: Fix handling of this special character in `RepositoryService`
const specialFilesToIgnore = (file: string) => {
  const regex = /"workhorse\/testdata\/file-[^/]*\.pdf"/;
  return regex.test(file) || file === 'workhorse/testdata/file-ä.pdf';
};