TestRenameAnonymousContainer: fix error msg

A recent CI run shows a (seemingly random) failure from this test:

> 00:14:37.289 --- FAIL: TestRenameAnonymousContainer (1.75s)
> 00:14:37.289 rename_test.go:169: assertion failed: 0 (int) != 1 (inspect.State.ExitCode int): container baac251d5a1cb2221ffedf6f10acbad166b90e3549601e96d908e76762675a81 exited with the wrong exitcode: {ContainerJSONBase:0xc0007a4840 Mounts:[] Config:0xc000714500 NetworkSettings:0xc000235b00}

Apparently, printing the whole `inspect` value does not make any sense.
Let's output `inspect.State.Error` instead, maybe it will help to
figure out what is going on here.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

integration/container/rename_test.go

@@ -165,7 +165,7 @@ func TestRenameAnonymousContainer(t *testing.T) {
 
 	inspect, err := client.ContainerInspect(ctx, cID)
 	assert.NilError(t, err)
-	assert.Check(t, is.Equal(0, inspect.State.ExitCode), "container %s exited with the wrong exitcode: %+v", cID, inspect)
+	assert.Check(t, is.Equal(0, inspect.State.ExitCode), "container %s exited with the wrong exitcode: %s", cID, inspect.State.Error)
 }
 
 // TODO: should be a unit test