vim-patch:9.1.0583: filetype: *.pdf_tex files are not recognized

Problem:  filetype: *.pdf_tex files are not recognized
Solution: Detect '*.pdf_tex' files as tex filetype
          (Jonas Dujava)

Those files are generated by inkscape, when exporting, see e.g.
https://inkscape.org/doc/inkscape-man.html

closes: vim/vim#15250

28145e005d

Co-authored-by: Jonas Dujava <jonas.dujava@gmail.com>

runtime/lua/vim/filetype.lua

@@ -1076,6 +1076,7 @@ local extension = {
   nls = 'tex',
   thm = 'tex',
   eps_tex = 'tex',
+  pdf_tex = 'tex',
   pygtex = 'tex',
   pygstyle = 'tex',
   clo = 'tex',