runtime(vim): Update syntax file (#13969)

Improve string interpolation highlighting.

Use the vimSep group to highlight interpolation braces as vimOperParen
has no highlighting of its own and employs vimSep via matchgroup.

Add vimNumber to the interpolation group's contained list.

Signed-off-by: Doug Kearns <dougkearns@gmail.com>
Signed-off-by: thinca <thinca@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/syntax/vim.vim b/runtime/syntax/vim.vim
index 2179953..e9feb35 100644
--- a/runtime/syntax/vim.vim
+++ b/runtime/syntax/vim.vim
@@ -377,7 +377,7 @@
 
 syn region	vimString start=+$'+ end=+'+ skip=+''+ oneline contains=vimStringInterpolationBrace,vimStringInterpolationExpr
 syn region	vimString start=+$"+ end=+"+ oneline contains=@vimStringGroup,vimStringInterpolationBrace,vimStringInterpolationExpr
-syn region	vimStringInterpolationExpr matchgroup=vimOperParen start=+{+ end=+}+ oneline contains=vimFunc,vimFuncVar,vimOper,vimNotation,vimOperParen,vimString,vimVar
+syn region	vimStringInterpolationExpr matchgroup=vimSep start=+{+ end=+}+ oneline contains=vimFunc,vimFuncVar,vimOper,vimOperParen,vimNotation,vimNumber,vimString,vimVar
 syn match	vimStringInterpolationBrace "{{"
 syn match	vimStringInterpolationBrace "}}"