Fixes compilation on Clang 19.
Patch by Marco Rebhan <me@dblsaiko.net>
Fixes https://bugs.gentoo.org/940764

Signed-off-by: Gavin D. Howard <gavin@gavinhoward.com>

--- a/include/olm/list.hh
+++ b/include/olm/list.hh
@@ -99,7 +99,7 @@ public:
             return *this;
         }
         T * this_pos = _data;
-        T * const other_pos = other._data;
+        T const * other_pos = other._data;
         while (other_pos != other._end) {
             *this_pos = *other;
             ++this_pos;