DOC Set 1.5.1 release month (scikit-learn#29377)

Author: jeremiedbb

doc/templates/index.html

@@ -207,6 +207,7 @@ <h4 class="sk-card-title card-title sk-vert-align" sk-align-name="title">
         <h4 class="sk-landing-call-header">News</h4>
         <ul class="sk-landing-call-list list-unstyled">
           <li><strong>On-going development:</strong> <a href="whats_new/v1.6.html#version-1-6-0">scikit-learn 1.6 (Changelog)</a>.</li>
+          <li><strong>July 2024.</strong> scikit-learn 1.5.1 is available for download (<a href="whats_new/v1.5.html#version-1-5-1">Changelog</a>).</li>
           <li><strong>May 2024.</strong> scikit-learn 1.5.0 is available for download (<a href="whats_new/v1.5.html#version-1-5-0">Changelog</a>).</li>
           <li><strong>April 2024.</strong> scikit-learn 1.4.2 is available for download (<a href="whats_new/v1.4.html#version-1-4-2">Changelog</a>).</li>
           <li><strong>February 2024.</strong> scikit-learn 1.4.1.post1 is available for download (<a href="whats_new/v1.4.html#version-1-4-1-post1">Changelog</a>).</li>

doc/whats_new/v1.5.rst

@@ -18,7 +18,7 @@ For a short description of the main highlights of the release, please refer to
 Version 1.5.1
 =============
 
-**TODO**
+**July 2024**
 
 Changes impacting many modules
 ------------------------------