fix(filetype): fix typo (#37286)

Follow-up to #37278.

Not sure how I missed the typo. I even remember checking the PR twice...

runtime/lua/vim/filetype.lua

@@ -849,7 +849,7 @@ local extension = {
   NSS = 'natural',
   ncf = 'ncf',
   nginx = 'nginx',
-  ncl = 'nickle',
+  ncl = 'nickel',
   nim = 'nim',
   nims = 'nim',
   nimble = 'nim',

test/old/testdir/test_filetype.vim

@@ -577,7 +577,7 @@ func s:GetFilenameChecks() abort
     \ 'neomuttrc': ['Neomuttrc', '.neomuttrc', '.neomuttrc-file', '/.neomutt/neomuttrc', '/.neomutt/neomuttrc-file', 'Neomuttrc', 'Neomuttrc-file', 'any/.neomutt/neomuttrc', 'any/.neomutt/neomuttrc-file', 'neomuttrc', 'neomuttrc-file'],
     \ 'netrc': ['.netrc'],
     \ 'nginx': ['file.nginx', 'nginxfile.conf', 'filenginx.conf', 'any/etc/nginx/file', 'any/usr/local/nginx/conf/file', 'any/nginx/file.conf'],
-    \ 'nickle': ['file.ncl'],
+    \ 'nickel': ['file.ncl'],
     \ 'nim': ['file.nim', 'file.nims', 'file.nimble'],
     \ 'ninja': ['file.ninja'],
     \ 'nix': ['file.nix'],