vim-patch:8.2.4664: Elvish files are not recognized (#17963)

Problem:    Elvish files are not recognized.
Solution:   Recognize .elv files. (Bruno Roque, closes vim/vim#10058)
c1658a196b

src/nvim/testdir/test_filetype.vim

@@ -168,6 +168,7 @@ let s:filename_checks = {
     \ 'eelixir': ['file.eex', 'file.leex'],
     \ 'elm': ['file.elm'],
     \ 'elmfilt': ['filter-rules'],
+    \ 'elvish': ['file.elv'],
     \ 'epuppet': ['file.epp'],
     \ 'erlang': ['file.erl', 'file.hrl', 'file.yaws'],
     \ 'eruby': ['file.erb', 'file.rhtml'],