Fix Ractor.make_shareable changing locals for Procs

	env_copy() uses rb_ary_delete_at() with a loop counting up while
	iterating through the list of read only locals. rb_ary_delete_at() can
	shift elements in the array to an index lesser than the loop index,
	causing locals to be missed and set to Qfalse in the returned
	environment.

	Iterate through the locals in reverse instead, this way the shifting
	never happens for locals that are yet to be visited and we process all
	the locals in the array.

	[Bug #18023]
	---
	 bootstraptest/test_ractor.rb | 22 ++++++++++++++++++++++
	 vm.c                         |  2 +-
	 2 files changed, 23 insertions(+), 1 deletion(-)