vim-patch:9.1.0971: filetype: SLNX files are not recognized

Problem:  filetype: SLNX files are not recognized
Solution: detect '*.slnx' files as xml filetype
          (Gustav Eikaas)

References:
https://blog.ndepend.com/slnx-the-new-net-solution-xml-file-format/
https://blog.jetbrains.com/dotnet/2024/10/04/support-for-slnx-solution-files/

closes: vim/vim#16334

3b3318b640

Co-authored-by: GustavEikaas <gustav.eikaas@gmail.com>

runtime/lua/vim/filetype.lua

@@ -1337,6 +1337,7 @@ local extension = {
   xlb = 'xml',
   xlc = 'xml',
   xba = 'xml',
+  slnx = 'xml',
   xpm = detect_line1('XPM2', 'xpm2', 'xpm'),
   xpm2 = 'xpm2',
   xqy = 'xquery',

test/old/testdir/test_filetype.vim

@@ -886,7 +886,7 @@ func s:GetFilenameChecks() abort
     \ 'xml': ['/etc/blkid.tab', '/etc/blkid.tab.old', 'file.xmi', 'file.csproj', 'file.csproj.user', 'file.fsproj', 'file.fsproj.user', 'file.vbproj', 'file.vbproj.user', 'file.ui',
     \         'file.tpm', '/etc/xdg/menus/file.menu', 'fglrxrc', 'file.xlf', 'file.xliff', 'file.xul', 'file.wsdl', 'file.wpl', 'any/etc/blkid.tab', 'any/etc/blkid.tab.old',
     \         'any/etc/xdg/menus/file.menu', 'file.atom', 'file.rss', 'file.cdxml', 'file.psc1', 'file.mpd', 'fonts.conf', 'file.xcu', 'file.xlb', 'file.xlc', 'file.xba', 'file.xpr',
-    \         'file.xpfm', 'file.spfm', 'file.bxml', 'file.mmi'],
+    \         'file.xpfm', 'file.spfm', 'file.bxml', 'file.mmi', 'file.slnx'],
     \ 'xmodmap': ['anyXmodmap', 'Xmodmap', 'some-Xmodmap', 'some-xmodmap', 'some-xmodmap-file', 'xmodmap', 'xmodmap-file'],
     \ 'xpm': ['file.xpm'],
     \ 'xpm2': ['file.xpm2'],