message: Fix `sticky-file-header` positioning
diff: -/* `.sticky-file-header` excludes native sticky header */
  -.file-header:not(.sticky-file-header) {
  +:root .file-header {
  position: sticky;
  - top: 60px;
  + z-index: 6; /* isBlame, isEditingFile */
  + top: 0;
  }
  -.notification-shelf ~ .application-main .file-header:not(.sticky-file-header) {
  +.notification-shelf ~ .application-main .file-header {
  top: 129px;
  }
  +
  +/* Consider the File List fixed header/sidebar in commits */
  +:root diff-layout .file-header {
  + top: 60px;
  +}
  +
  +/*
  +Test URLs
  +https://github.com/refined-github/refined-github/commit/1d9dd9f0208c327351512beb6d6a22279bc47807
  +https://github.com//refined-github/refined-github/compare/22.2.13...22.2.22#files_bucket
  +https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c
  +https://github.com/refined-github/refined-github/edit/main/readme.md
  +https://github.com/refined-github/refined-github/blame/243e51d786e4771d313091b94cec826ff86becc9/source/features/index.tsx#L326-L327
  +
  +Exclude:
  +https://github.com/refined-github/refined-github/pull/5460/files (actually included, but natively supported anyway)
  +*/
  