Backport of the following commit to 0.5:

From 2a63206b00ee364780dec377d691a1a26624ca34 Mon Sep 17 00:00:00 2001
From: Ewoud Kohl van Wijngaarden <ewoud@kohlvanwijngaarden.nl>
Date: Tue, 30 Jul 2024 23:47:30 +0200
Subject: [PATCH] Fix Ruby 3.2 warning about undefined allocator (#14)

This fixes 'warning: undefining the allocator of T_DATA class Augeas'
which Ruby 3.2 started to warn about.

See https://bugs.ruby-lang.org/issues/18007 for more information.

--- ruby-augeas-0.5.0+gem.orig/ext/augeas/_augeas.c
+++ ruby-augeas-0.5.0+gem/ext/augeas/_augeas.c
@@ -489,6 +489,7 @@ void Init__augeas() {
 
     /* Define the ruby class */
     c_augeas = rb_define_class("Augeas", rb_cObject) ;
+    rb_undef_alloc_func(c_augeas);
 
     /* Constants for enum aug_flags */
 #define DEF_AUG_FLAG(name) \