fix(runtime): source old color scheme in bundled color schemes (#26641)

Problem:
Bundled color schemes use `:hi clear` and only define Vim's highlight
groups. This results into Nvim-specific highlight groups using
definitions from Nvim's default color scheme, which are not always
linked to a Vim's highlight group.

Solution:
Restore links to Vim's highlight groups which were present before Nvim's
default color scheme update.

runtime/colors/torte.vim

@@ -10,7 +10,8 @@
 
 set background=dark
 
-hi clear
+" hi clear
+source $VIMRUNTIME/colors/vim.lua " Nvim: revert to Vim default color scheme
 let g:colors_name = 'torte'
 
 let s:t_Co = &t_Co