bpo-31787: Prevent refleaks when calling __init__() more than once (GH-3995)

(cherry picked from commit d019bc8319ea35e93bf4baa38098ff1b57cd3ee5)

Co-authored-by: Oren Milman <orenmn@gmail.com>
diff --git a/Lib/test/test_hashlib.py b/Lib/test/test_hashlib.py
index 751f748..f7df872 100644
--- a/Lib/test/test_hashlib.py
+++ b/Lib/test/test_hashlib.py
@@ -162,6 +162,15 @@
         constructors = self.constructors_to_test.values()
         return itertools.chain.from_iterable(constructors)
 
+    @support.refcount_test
+    def test_refleaks_in_hash___init__(self):
+        gettotalrefcount = support.get_attribute(sys, 'gettotalrefcount')
+        sha1_hash = c_hashlib.new('sha1')
+        refs_before = gettotalrefcount()
+        for i in range(100):
+            sha1_hash.__init__('sha1')
+        self.assertAlmostEqual(gettotalrefcount() - refs_before, 0, delta=10)
+
     def test_hash_array(self):
         a = array.array("b", range(10))
         for cons in self.hash_constructors: