Fix tf-addons for upcoming keras 3 default.

[cantonios]

Description

Keras 3.0 will become default in TF 2.16 (and is currently default in tf-nightly). This breaks this tf-addons package. Here we make minimal changes to return functionality in a backward-compatible way.

Fixes # (issue)

None known reported.

Type of change

• [X] Bug fix

Checklist:

• [X] I've properly formatted my code according to the guidelines
  • [] By running Black + Flake8
  • [X] By running pre-commit hooks
• [ ] This PR addresses an already submitted issue for TensorFlow Addons
• [ ] I have made corresponding changes to the documentation
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] This PR contains modifications to C++ custom-ops

How Has This Been Tested?

Imported with tf-nightly, keras-nightly, tf_keras-nightly, setting both TF_USE_LEGACY_KERAS=0 and 1.

[bot-of-gabrieldemarmiesse]

@howl-anderson @pedrolarben @ssaishruthi @hyang0129

You are owners of some files modified in this pull request. Would you kindly review the changes whenever you have the time to? Thank you very much.