Fix release date

Author: Ericgig

_includes/sidebar.html

@@ -6,7 +6,7 @@
   <div class="panel-body">
          <strong>QuTiP 5.0.4</strong>:
          <ul>
-           <li>June 28, 2024</li>
+           <li>September 03, 2024</li>
            <li><a href="https://qutip.readthedocs.io/en/qutip-5.0.x/installation.html">install</a></li>
            <li><a href="https://qutip.readthedocs.io/en/qutip-5.0.x/">docs</a></li>
            <li><a href="https://github.com/qutip/qutip/releases/tag/v5.0.4">src</a></li>