vim-patch:8.2.3285: scdoc filetype is not recognized (#15294)

Problem:    Scdoc filetype is not recognized.
Solution:   Add filetype detection. (Gregory Anders, closes vim/vim#8701)
dd097bdc13

src/nvim/testdir/test_filetype.vim

@@ -431,6 +431,7 @@ let s:filename_checks = {
     \ 'scilab': ['file.sci', 'file.sce'],
     \ 'screen': ['.screenrc', 'screenrc'],
     \ 'sexplib': ['file.sexp'],
+    \ 'scdoc': ['file.scd'],
     \ 'scss': ['file.scss'],
     \ 'sd': ['file.sd'],
     \ 'sdc': ['file.sdc'],