CI warning: tensorflow: graph support has been removed in eager mode

```
tests/explainers/test_deep.py::test_tf_keras_mnist_cnn
tests/explainers/test_deep.py::test_tf_keras_linear
  Your TensorFlow version is newer than 2.4.0 and so graph support has been removed in eager mode and some static graphs may not be supported. See PR #1483 for discussion.

```