tests/exec: expect 127 exit code for missing executable

Docker Engine has always returned `126` when starting an exec fails due
to a missing binary, but this was due to a bug in the daemon causing the
correct exit code to be overwritten in some cases – see: moby/moby#45795

Change tests to expect correct exit code (`127`).

Signed-off-by: Laura Brehm <[email protected]>

tests/integration/models_containers_test.py

@@ -360,7 +360,7 @@ def test_exec_run_failed(self):
         )
         self.tmp_containers.append(container.id)
         exec_output = container.exec_run("docker ps")
-        assert exec_output[0] == 126
+        assert exec_output[0] == 127
 
     def test_kill(self):
         client = docker.from_env(version=TEST_API_VERSION)