cli/command: TestRetrieveAuthTokenFromImage: don't decode authconfig

Rewrite the test to not depend on registry.DecodeAuthConfig, which
may be moved internal to the daemon as part of the modules transition.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit ae1727c41e)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/command/registry_test.go

@@ -185,9 +185,9 @@ func TestRetrieveAuthTokenFromImage(t *testing.T) {
 				imageRef := path.Join(tc.prefix, remoteRef)
 				actual, err := command.RetrieveAuthTokenFromImage(&cfg, imageRef)
 				assert.NilError(t, err)
-				ac, err := registry.DecodeAuthConfig(actual)
+				expectedAuthCfg, err := registry.EncodeAuthConfig(tc.expectedAuthCfg)
 				assert.NilError(t, err)
-				assert.Check(t, is.DeepEqual(*ac, tc.expectedAuthCfg))
+				assert.Equal(t, actual, expectedAuthCfg)
 			}
 		})
 	}