merge revision(s) 417b1a36447cb2c650de55b433ba623541fb8bb3: [Backport #19550]

	Fix memory leak for iclass

	[Bug #19550]

	If !RCLASS_EXT_EMBEDDED (e.g. 32 bit systems) then the rb_classext_t is
	allocated throug malloc so it must be freed.

	The issue can be seen in the following script:

	```
	20.times do
	  100_000.times do
	    mod = Module.new
	    Class.new do
	      include mod
	    end
	  end

	  # Output the Resident Set Size (memory usage, in KB) of the current Ruby process
	  puts `ps -o rss= -p #{$$}`
	end
	```

	Before this fix, the max RSS is 280MB, while after this change, it's
	30MB.
	---
	 gc.c                     |  2 +-
	 test/ruby/test_module.rb | 15 +++++++++++++++
	 2 files changed, 16 insertions(+), 1 deletion(-)

0 files changed, 0 insertions, 0 deletions