vim-patch:9.1.0396: filetype: jj files are not recognized (#28672)

Problem:  jj files are not recognized
Solution: recognize '*.jjdescription' files as jj filetype
          (Gregory Anders)

See: https://github.com/martinvonz/jj

closes: vim/vim#14733

6a4ea471d2

test/old/testdir/test_filetype.vim

@@ -360,6 +360,7 @@ func s:GetFilenameChecks() abort
     \ 'javascriptreact': ['file.jsx'],
     \ 'jess': ['file.clp'],
     \ 'jgraph': ['file.jgr'],
+    \ 'jj': ['file.jjdescription'],
     \ 'jq': ['file.jq'],
     \ 'jovial': ['file.jov', 'file.j73', 'file.jovial'],
     \ 'jproperties': ['file.properties', 'file.properties_xx', 'file.properties_xx_xx', 'some.properties_xx_xx_file', 'org.eclipse.xyz.prefs'],