fix(windows): consistent normalization in fs.find

vim.fs.find(".luacheckrc")

```
c:\\projects\\neovim/.luacheckrc # before

c:/projects/neovim/.luacheckrc   # after
```

Co-authored-by: kylo252 <59826753+kylo252@users.noreply.github.com>

runtime/lua/vim/fs.lua

@@ -216,7 +216,7 @@ function M.find(names, opts)
 
   ---@private
   local function add(match)
-    matches[#matches + 1] = match
+    matches[#matches + 1] = M.normalize(match)
     if #matches == limit then
       return true
     end