ruby: fix "undefining the allocator of T_DATA" warnings

Ruby 3.2 introduced a warning when C-extensions use structs without
redefining the allocation default allocation routine meant for objects.
See https://bugs.ruby-lang.org/issues/18007 for details.

In the Ruby bindings this happens at `Data_Wrap_Notmuch_Object` call
sites, so the object types used there needed to update their allocation.

This ruby code (given a database at the hardcoded path with messages
matching `tag:tmp`) exercise all the ruby objects:

    require 'notmuch'
    Notmuch::Database.open File.expand_path("~/mail") do |db|
      db.get_directory("/tmp")
      db.query("tag:tmp").search_threads.each do |t|
        t.messages.each do |m|
          puts m.header("Subject")
        end
      end
    end

Before these changes with ruby 3.2.5 and notmuch 0.38.3 it outputs:

    notmuch.rb:5: warning: undefining the allocator of T_DATA class Notmuch::Query
    notmuch.rb:5: warning: undefining the allocator of T_DATA class Notmuch::Threads
    notmuch.rb:5: warning: undefining the allocator of T_DATA class Notmuch::Thread
    notmuch.rb:6: warning: undefining the allocator of T_DATA class Notmuch::Messages
    notmuch.rb:6: warning: undefining the allocator of T_DATA class Notmuch::Message
    notmuch release 0.38.3 now available

(the last line is the message I tagged with tmp), and after the changes:

    notmuch release 0.38.3 now available

1 files changed, 5 insertions, 0 deletions

diff --git a/bindings/ruby/init.c b/bindings/ruby/init.c
index 2d1994af..10558a33 100644
--- a/bindings/ruby/init.c
+++ b/bindings/ruby/init.c
@@ -293,6 +293,7 @@ Init_notmuch (void)
      * Notmuch query
      */
     notmuch_rb_cQuery = rb_define_class_under (mod, "Query", rb_cObject);
+    rb_undef_alloc_func(notmuch_rb_cQuery);
     rb_undef_method (notmuch_rb_cQuery, "initialize");
     rb_define_method (notmuch_rb_cQuery, "destroy!", notmuch_rb_query_destroy, 0); /* in query.c */
     rb_define_method (notmuch_rb_cQuery, "sort", notmuch_rb_query_get_sort, 0); /* in query.c */
@@ -311,6 +312,7 @@ Init_notmuch (void)
      * Notmuch threads
      */
     notmuch_rb_cThreads = rb_define_class_under (mod, "Threads", rb_cObject);
+    rb_undef_alloc_func(notmuch_rb_cThreads);
     rb_undef_method (notmuch_rb_cThreads, "initialize");
     rb_define_method (notmuch_rb_cThreads, "destroy!", notmuch_rb_threads_destroy, 0); /* in threads.c */
     rb_define_method (notmuch_rb_cThreads, "each", notmuch_rb_threads_each, 0); /* in threads.c */
@@ -322,6 +324,7 @@ Init_notmuch (void)
      * Notmuch messages
      */
     notmuch_rb_cMessages = rb_define_class_under (mod, "Messages", rb_cObject);
+    rb_undef_alloc_func(notmuch_rb_cMessages);
     rb_undef_method (notmuch_rb_cMessages, "initialize");
     rb_define_method (notmuch_rb_cMessages, "destroy!", notmuch_rb_messages_destroy, 0); /* in messages.c */
     rb_define_method (notmuch_rb_cMessages, "each", notmuch_rb_messages_each, 0); /* in messages.c */
@@ -334,6 +337,7 @@ Init_notmuch (void)
      * Notmuch thread
      */
     notmuch_rb_cThread = rb_define_class_under (mod, "Thread", rb_cObject);
+    rb_undef_alloc_func(notmuch_rb_cThread);
     rb_undef_method (notmuch_rb_cThread, "initialize");
     rb_define_method (notmuch_rb_cThread, "destroy!", notmuch_rb_thread_destroy, 0); /* in thread.c */
     rb_define_method (notmuch_rb_cThread, "thread_id", notmuch_rb_thread_get_thread_id, 0); /* in thread.c */
@@ -353,6 +357,7 @@ Init_notmuch (void)
      * Notmuch message
      */
     notmuch_rb_cMessage = rb_define_class_under (mod, "Message", rb_cObject);
+    rb_undef_alloc_func(notmuch_rb_cMessage);
     rb_undef_method (notmuch_rb_cMessage, "initialize");
     rb_define_method (notmuch_rb_cMessage, "destroy!", notmuch_rb_message_destroy, 0); /* in message.c */
     rb_define_method (notmuch_rb_cMessage, "message_id", notmuch_rb_message_get_message_id, 0); /* in message.c */