fix(lua): highlight.on_yank can close timer in twice #18976

Steps to reproduce:

1. setting `vim.highlight.on_yank`
   ```
   vim.api.nvim_create_autocmd({ "TextYankPost" }, {
     pattern = { "*" },
     callback = function()
       vim.highlight.on_yank({ timeout = 200 })
     end,
   })
   ```
2. repeat typing `yeye` ...
3. causes the following error.
   ```
   Error executing vim.schedule lua callback: vim/_editor.lua:0: handle 0x01e96970 is already closing
   stack traceback:
           [C]: in function 'close'
           vim/_editor.lua: in function ''
           vim/_editor.lua: in function <vim/_editor.lua:0>
   ```

📝 Test result before fix:

    [----------] Global test environment setup.
    [----------] Running tests from test/functional/lua/highlight_spec.lua
    [ RUN      ] vim.highlight.on_yank does not show errors even if buffer is wiped before timeout: 15.07 ms OK
    [ RUN      ] vim.highlight.on_yank does not show errors even if executed between timeout and clearing highlight: 15.07 ms ERR
    test/helpers.lua:73: Expected objects to be the same.
    Passed in:
    (string) 'Error executing vim.schedule lua callback: vim/_editor.lua:0: handle 0x02025260 is already closing
    stack traceback:
            [C]: in function 'close'
            vim/_editor.lua: in function ''
            vim/_editor.lua: in function <vim/_editor.lua:0>'
    Expected:
    (string) ''

runtime/lua/vim/_editor.lua

@@ -408,7 +408,9 @@ function vim.defer_fn(fn, timeout)
     timeout,
     0,
     vim.schedule_wrap(function()
+      if not timer:is_closing() then
         timer:close()
+      end
 
       fn()
     end)

test/functional/lua/highlight_spec.lua

@@ -6,20 +6,29 @@ local command = helpers.command
 local clear = helpers.clear
 
 describe('vim.highlight.on_yank', function()
-
   before_each(function()
     clear()
   end)
 
   it('does not show errors even if buffer is wiped before timeout', function()
     command('new')
-    exec_lua[[
+    exec_lua([[
       vim.highlight.on_yank({timeout = 10, on_macro = true, event = {operator = "y", regtype = "v"}})
       vim.cmd('bwipeout!')
-    ]]
+    ]])
     helpers.sleep(10)
     helpers.feed('<cr>') -- avoid hang if error message exists
     eq('', eval('v:errmsg'))
   end)
 
+  it('does not close timer twice', function()
+    exec_lua([[
+      vim.highlight.on_yank({timeout = 10, on_macro = true, event = {operator = "y"}})
+      vim.loop.sleep(10)
+      vim.schedule(function()
+        vim.highlight.on_yank({timeout = 0, on_macro = true, event = {operator = "y"}})
+      end)
+    ]])
+    eq('', eval('v:errmsg'))
+  end)
 end)