merge revision(s) 0b8f15575a440f85ac686f5b0eae8f8b7c2b72e7: [Backport #19836]

	Fix memory leak for incomplete lambdas

	[Bug #19836]

	The parser does not free the chain of `struct vtable`, which causes
	memory leaks.

	The following script reproduces this issue:

	```
	10.times do
	  100_000.times do
	    Ripper.parse("-> {")
	  end

	  puts `ps -o rss= -p #{$$}`
	end
	```
	---
	 parse.y                    | 24 ++++++++++++++----------
	 test/ripper/test_ripper.rb |  7 +++++++
	 2 files changed, 21 insertions(+), 10 deletions(-)

1 files changed, 22 insertions, 7 deletions

diff --git a/test/ripper/test_ripper.rb b/test/ripper/test_ripper.rb
index a9773a89d8..83b43d67fe 100644
--- a/test/ripper/test_ripper.rb
+++ b/test/ripper/test_ripper.rb
@@ -120,13 +120,6 @@ class TestRipper::Ripper < Test::Unit::TestCase
       END
       assert_nil(Ripper.sexp(src), bug12651)
     end;
-
-    # [Bug #19835]
-    assert_no_memory_leak(%w(-rripper), "", "#{<<~'end;'}", rss: true)
-      1_000_000.times do
-        Ripper.parse("class Foo")
-      end
-    end;
   end
 
   # https://bugs.jruby.org/4176
@@ -148,6 +141,28 @@ end
     assert_nothing_raised { Ripper.lex src }
   end
 
+  def test_no_memory_leak
+    assert_no_memory_leak(%w(-rripper), "", "#{<<~'end;'}", rss: true)
+      2_000_000.times do
+        Ripper.parse("")
+      end
+    end;
+
+    # [Bug #19835]
+    assert_no_memory_leak(%w(-rripper), "", "#{<<~'end;'}", rss: true)
+      1_000_000.times do
+        Ripper.parse("class Foo")
+      end
+    end;
+
+    # [Bug #19836]
+    assert_no_memory_leak(%w(-rripper), "", "#{<<~'end;'}", rss: true)
+      1_000_000.times do
+        Ripper.parse("-> {")
+      end
+    end;
+  end
+
   class TestInput < self
     Input = Struct.new(:lines) do
       def gets