Switched YAMNet to stick with Keras 2.

[plakal]

Description

Switched YAMNet to stick with Keras 2. TF 2.16 switched the default to Keras 3
which is backwards incompatible.

closes #11212

Type of change

For a new feature or function, please create an issue first to discuss it
with us before submitting a pull request.

Note: Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• Documentation update
• TensorFlow 2 migration
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• A new research paper code implementation
• Other (Specify)

Tests

Installed latest versions of all dependences (including new tf_keras) and
ran yamnet_test.py

Test Configuration:

Checklist

• I have signed the Contributor License Agreement.
• I have read guidelines for pull request.
• My code follows the coding guidelines.
• I have performed a self code review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• I have added tests that prove my fix is effective or that my feature works.

[dpwe]

LGTM. Thanks for figuring this out!