Update best-practices.rst: fix Connection.get -> Connection. get_conn…

…ection_from_secrets (apache#39560)

docs/apache-airflow/best-practices.rst

@@ -824,7 +824,7 @@ For connection, use :envvar:`AIRFLOW_CONN_{CONN_ID}`.
     )
     conn_uri = conn.get_uri()
     with mock.patch.dict("os.environ", AIRFLOW_CONN_MY_CONN=conn_uri):
-        assert "cat" == Connection.get("my_conn").login
+        assert "cat" == Connection.get_connection_from_secrets("my_conn").login
 
 Metadata DB maintenance
 ^^^^^^^^^^^^^^^^^^^^^^^