chore(render-markdown): use API to toggle (#6558)

## Description

The `state` module in `render-markdown` is not expected to be accessed
outside of the package and may be refactored in the future.

Prevent any breaking changes in LazyVim by using the public API which
was updated here:

accaa600ba

## Related Issue(s)

None

## Screenshots

N/A

## Checklist

- [x] I've read the
[CONTRIBUTING](https://github.com/LazyVim/LazyVim/blob/main/CONTRIBUTING.md)
guidelines.

lua/lazyvim/plugins/extras/lang/markdown.lua

@@ -113,17 +113,8 @@ return {
       require("render-markdown").setup(opts)
       Snacks.toggle({
         name = "Render Markdown",
-        get = function()
-          return require("render-markdown.state").enabled
-        end,
-        set = function(enabled)
-          local m = require("render-markdown")
-          if enabled then
-            m.enable()
-          else
-            m.disable()
-          end
-        end,
+        get = require("render-markdown").get,
+        set = require("render-markdown").set,
       }):map("<leader>um")
     end,
   },