vim-patch:9.1.0196: filetype: support for gnuplot files is lacking (#27972)

Problem:  filetype: support for gnuplot files is lacking
Solution: Also detect *.gnuplot files
          (RobbiZ98)

closes: vim/vim#14243

3a6bd0c5c7

Co-authored-by: RobbiZ98 <113035863+RobbiZ98@users.noreply.github.com>

runtime/lua/vim/filetype.lua

@@ -466,6 +466,7 @@ local extension = {
   glsl = 'glsl',
   gn = 'gn',
   gni = 'gn',
+  gnuplot = 'gnuplot',
   gpi = 'gnuplot',
   go = 'go',
   gp = 'gp',
@@ -1304,7 +1305,6 @@ local filename = {
   ['.gnashpluginrc'] = 'gnash',
   gnashpluginrc = 'gnash',
   gnashrc = 'gnash',
-  ['.gnuplot'] = 'gnuplot',
   ['go.sum'] = 'gosum',
   ['go.work.sum'] = 'gosum',
   ['go.work'] = 'gowork',