Fixed ResourceWarning from unclosed SQLite connection on Python 3.13+.

- backends.sqlite.tests.ThreadSharing.test_database_sharing_in_threads
- backends.tests.ThreadTests.test_default_connection_thread_local:
    on SQLite, close() doesn't explicitly close in-memory connections.
- servers.tests.LiveServerInMemoryDatabaseLockTest
- test_runner.tests.SQLiteInMemoryTestDbs.test_transaction_support

Check out https://github.com/python/cpython/pull/108015.

tests/servers/tests.py

@@ -115,6 +115,7 @@ class LiveServerInMemoryDatabaseLockTest(LiveServerBase):
         connection.
         """
         conn = self.server_thread.connections_override[DEFAULT_DB_ALIAS]
+        source_connection = conn.connection
         # Open a connection to the database.
         conn.connect()
         # Create a transaction to lock the database.
@@ -128,6 +129,7 @@ class LiveServerInMemoryDatabaseLockTest(LiveServerBase):
         finally:
             # Release the transaction.
             cursor.execute("ROLLBACK")
+            source_connection.close()
 
 
 class FailingLiveServerThread(LiveServerThread):