[oct-hdf5] point the install instructions at tag git20260830

That tag carries the fix that stops oct-hdf5 from passing "-lmpi" through from
Octave HDF5_LIBS when libmpi is not linkable, so it installs on a plain
Debian/Ubuntu machine without an MPI development package. Users following the
message printed by saveh5/loadh5 hit exactly the link failure the older tag
produced, so the URL is bumped there as well.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: fangq

loadh5.m

@@ -79,7 +79,7 @@
         end
     catch
         error(['To use EasyH5 in Octave, one must install oct-hdf5 first using\n\t' ...
-               'pkg install https://github.com/NeuroJSON/oct-hdf5/archive/refs/tags/git20250413.zip\n%s'], '');
+               'pkg install https://github.com/NeuroJSON/oct-hdf5/archive/refs/tags/git20260830.zip\n%s'], '');
     end
 end
 

saveh5.m

@@ -97,7 +97,7 @@ function saveh5(data, fname, varargin)
         pkg load oct-hdf5;
     catch
         error(['To use EasyH5 in Octave, one must install oct-hdf5 first using\n\t' ...
-               'pkg install https://github.com/NeuroJSON/oct-hdf5/archive/refs/tags/git20250413.zip\n%s'], '');
+               'pkg install https://github.com/NeuroJSON/oct-hdf5/archive/refs/tags/git20260830.zip\n%s'], '');
     end
 end