Fixed #25454 -- Ensured register_hstore_handler is called for all connections

Thanks Simon Charette for help with the patch.

tests/postgres_tests/__init__.py

@@ -1,9 +1,16 @@
 import unittest
 
 from django.db import connection
+from django.db.backends.signals import connection_created
 from django.test import TestCase
 
 
 @unittest.skipUnless(connection.vendor == 'postgresql', "PostgreSQL specific tests")
 class PostgreSQLTestCase(TestCase):
-    pass
+    @classmethod
+    def tearDownClass(cls):
+        # No need to keep that signal overhead for non PostgreSQL-related tests.
+        from django.contrib.postgres.signals import register_hstore_handler
+
+        connection_created.disconnect(register_hstore_handler)
+        super(PostgreSQLTestCase, cls).tearDownClass()