add tensorflow as the KERAS_BACKEND for qkerasV3 tests

[jmitrevs]

Description

This should fix the qkeras3 pytests issues introduced with qkeras_v3==1.2

Type of change

QKeras v3 1.2 needs to have the KERAS_BACKEND environment variable set, so this sets it in the CI.

• Bug fix (non-breaking change that fixes an issue)
• Other (Specify) - CI

Tests

This is a CI fix so it will only be visible in the CI. Compare with the qkeras3 pytest in #1497.

Checklist

• I have read the guidelines for contributing.
• 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 installed and run pre-commit on the files I edited or added.
• I have added tests that prove my fix is effective or that my feature works.

[calad0i]

Sounds like a bug from upstream in qkeras v3 to me. In keras v3, if KERAS_BACKEND is not set, it shall be regarded as tensorflow.

[jmitrevs]

However, we need a workaround till it is fixed. It seems better to explicitly set it vs to lock the version to an older version of qkeras3.

[calad0i]

I would do version lock in this case

[jmitrevs]

I don't have a strong preference either way. Let's see what others say. I don't see a particular downside in setting the KERAS_BACKEND explicitly.

[makoeppel]

I can set the backend default to tensorflow in qkerasv3.

[makoeppel]

I fixed the default backend to tensorflow in qkerasv3.