fix(toggle): make diagnostics compatible with nvim-0.9.5 (#4205)

## Description
This makes `toggle.diagnostics` compatible with Neovim 0.9.5 (though not
sure about the metatable callables, since `set` there accepts a boolean
from `get` state).

Please make whatever changes you deem necessary or disregard as a whole
for a better approach I haven't been able to think of.
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  why we should accept this pull request. -->

## Related Issue(s)
Fixes #4203
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  If this PR fixes any issues, please link to the issue here.
  - Fixes #<issue_number>
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## Screenshots

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## Checklist

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

lua/lazyvim/util/toggle.lua

@@ -127,9 +127,32 @@ M.number = M.wrap({
 M.diagnostics = M.wrap({
   name = "Diagnostics",
   get = function()
-    return vim.diagnostic.is_enabled and vim.diagnostic.is_enabled()
+    local enabled
+    if vim.diagnostic.is_enabled then
+      enabled = vim.diagnostic.is_enabled()
+    else
+      enabled = not vim.diagnostic.is_disabled()
+    end
+    return enabled
+  end,
+  set = function()
+    local enabled
+    if vim.diagnostic.is_enabled then
+      enabled = vim.diagnostic.is_enabled()
+    else
+      enabled = not vim.diagnostic.is_disabled()
+    end
+    enabled = not enabled
+    if vim.fn.has("nvim-0.10") == 0 then
+      if enabled then
+        pcall(vim.diagnostic.enable)
+      else
+        vim.diagnostic.disable()
+      end
+    else
+      vim.diagnostic.enable(enabled)
+    end
   end,
-  set = vim.diagnostic.enable,
 })
 
 M.inlay_hints = M.wrap({