http_gate: Fix test_object2_can_be_get_by_attr

Test modified to be consistent with the http-gw change:
nspcc-dev/neofs-http-gw@e6e7941

Changed the expected error from "object already removed" to "404 Not Found"
when trying to get a previously removed object.

Signed-off-by: Oleg Kulachenko <oleg@nspcc.ru>

pytest_tests/testsuites/services/http_gate/test_http_headers.py

@@ -25,7 +25,6 @@
 from helpers.storage_object_info import StorageObjectInfo
 from steps.cluster_test_base import ClusterTestBase
 
-OBJECT_ALREADY_REMOVED_ERROR = "object already removed"
 logger = logging.getLogger("NeoLogger")
 
 
@@ -146,10 +145,11 @@ def test_object2_can_be_get_by_attr(
                 shell=self.shell,
                 endpoint=self.cluster.default_rpc_endpoint,
             )
+            error_pattern = "404 Not Found"
             try_to_get_object_and_expect_error(
                 cid=storage_object_2.cid,
                 oid=storage_object_2.oid,
-                error_pattern=OBJECT_ALREADY_REMOVED_ERROR,
+                error_pattern=error_pattern,
                 endpoint=self.cluster.default_http_gate_endpoint,
             )
             storage_objects_with_attributes.remove(storage_object_2)