tests: fix test_find_path_for_payment. need to close sqlite connection

test was sometimes randomly failing
(always on Windows, as it's illegal to rm open files there)

electrum/sql_db.py

@@ -54,4 +54,5 @@ class SqlDB(Logger):
                     self.conn.commit()
         # write
         self.conn.commit()
+        self.conn.close()
         self.logger.info("SQL thread terminated")