doc: add tooltip for light/dark mode toggle

PR-URL: #37044
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

doc/template.html

@@ -25,7 +25,7 @@
       <header>
         <div class="header-container">
           <h1>Node.js __VERSION__ Documentation</h1>
-          <button class="theme-toggle-btn" id="theme-toggle-btn" aria-label="Toggle dark mode/light mode" hidden>
+          <button class="theme-toggle-btn" id="theme-toggle-btn" title="Toggle dark mode/light mode" aria-label="Toggle dark mode/light mode" hidden>
             <svg xmlns="http://www.w3.org/2000/svg" class="icon dark-icon" height="24" width="24">
               <path fill="none" d="M0 0h24v24H0z" />
               <path d="M11.1 12.08c-2.33-4.51-.5-8.48.53-10.07C6.27 2.2 1.98 6.59 1.98 12c0 .14.02.28.02.42.62-.27 1.29-.42 2-.42 1.66 0 3.18.83 4.1 2.15A4.01 4.01 0 0111 18c0 1.52-.87 2.83-2.12 3.51.98.32 2.03.5 3.11.5 3.5 0 6.58-1.8 8.37-4.52-2.36.23-6.98-.97-9.26-5.41z"/>