merge revision(s) bbedd29b6e98ef6e3fc2ce2b358d2b509b7cd1bb: [Backport #18117]

	[Bug #18117] Fix Ractor race condition with GC

	rb_objspace_reachable_objects_from requires that the GC not be active.
	Since the Ractor barrier is not executed for incremental sweeping,
	Ractor may call rb_objspace_reachable_objects_from after sweeping
	has started to share objects. This causes a crash that looks like
	the following:

	```
	<internal:ractor>:627: [BUG] rb_objspace_reachable_objects_from() is not supported while during_gc == true
	```

	Co-authored-by: Vinicius Stock <vinicius.stock@shopify.com>
	---
	 bootstraptest/test_ractor.rb | 15 +++++++++++++++
	 ractor.c                     | 12 ++++++++++--
	 2 files changed, 25 insertions(+), 2 deletions(-)

1 files changed, 15 insertions, 0 deletions

diff --git a/bootstraptest/test_ractor.rb b/bootstraptest/test_ractor.rb
index cbf58383c7..f733877319 100644
--- a/bootstraptest/test_ractor.rb
+++ b/bootstraptest/test_ractor.rb
@@ -1379,4 +1379,19 @@ assert_equal "ok", %q{
   end
 }
 
+# Can yield back values while GC is sweeping [Bug #18117]
+assert_equal "ok", %q{
+  workers = (0...8).map do
+    Ractor.new do
+      loop do
+        10_000.times.map { Object.new }
+        Ractor.yield Time.now
+      end
+    end
+  end
+
+  1_000.times { idle_worker, tmp_reporter = Ractor.select(*workers) }
+  "ok"
+}
+
 end # if !ENV['GITHUB_WORKFLOW']