Windows package / snapshot: bump to Octave version 8.4.0

_includes/download-snapshot.html

@@ -19,7 +19,7 @@
     <p>
       Compatible with Windows (10 and 11), MATLAB (R2014a–R2023b) and
       GNU Octave
-      (<a href="https://ftp.gnu.org/gnu/octave/windows/octave-8.3.0-w64-installer.exe">8.3.0</a>
+      (<a href="https://ftp.gnu.org/gnu/octave/windows/octave-8.4.0-w64-installer.exe">8.4.0</a>
       only), 64-bit
     </p>