vim-patch:9.1.0108: filetype: no support for dtso files

Problem:  filetype: no support for dtso files
Solution: Add detection for *.dtso files as dts file type
          (Markus Schneider-Pargmann)

*.dtso files are devicetree overlay files which have the same syntax as dts or dtsi files.

closes: vim/vim#14026

b1700fb33f

Co-authored-by: Markus Schneider-Pargmann <msp@baylibre.com>

runtime/lua/vim/filetype.lua

@@ -364,6 +364,7 @@ local extension = {
   d = detect.dtrace,
   dts = 'dts',
   dtsi = 'dts',
+  dtso = 'dts',
   dylan = 'dylan',
   intr = 'dylanintr',
   lid = 'dylanlid',

test/old/testdir/test_filetype.vim

@@ -204,7 +204,7 @@ func s:GetFilenameChecks() abort
     \ 'dracula': ['file.drac', 'file.drc', 'filelvs', 'filelpe', 'drac.file', 'lpe', 'lvs', 'some-lpe', 'some-lvs'],
     \ 'dtd': ['file.dtd'],
     \ 'dtrace': ['/usr/lib/dtrace/io.d'],
-    \ 'dts': ['file.dts', 'file.dtsi'],
+    \ 'dts': ['file.dts', 'file.dtsi', 'file.dtso'],
     \ 'dune': ['jbuild', 'dune', 'dune-project', 'dune-workspace'],
     \ 'dylan': ['file.dylan'],
     \ 'dylanintr': ['file.intr'],