Bump keras from 2.3.1 to 2.4.2 in /cvat/requirements

[dependabot-preview]

Bumps keras from 2.3.1 to 2.4.2.

Release notes

Sourced from keras's releases.

Keras 2.4.0

As previously announced, we have discontinued multi-backend Keras to refocus exclusively on the TensorFlow implementation of Keras.

In the future, we will develop the TensorFlow implementation of Keras in the present repo, at keras-team/keras. For the time being, it is being developed in tensorflow/tensorflow and distributed as tensorflow.keras. In this future, the keras package on PyPI will be the same as tf.keras.

This release (2.4.0) simply redirects all APIs in the standalone keras package to point to tf.keras. This helps address user confusion regarding differences and incompatibilities between tf.keras and the standalone keras package. There is now only one Keras: tf.keras.

• Note that this release may be breaking for some workflows when going from Keras 2.3.1 to 2.4.0. Test before upgrading.
• Note that we still recommend that you import Keras as from tensorflow import keras, rather than import keras, for the time being.

Commits

• See full diff in compare view

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[coveralls]

Pull Request Test Coverage Report for Build 5943

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.004%) to 65.822%

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Files with Coverage Reduction	New Missed Lines	%
cvat/apps/engine/media_extractors.py	1	77.35%

Totals
Change from base Build 5929:	0.004%
Covered Lines:	10916
Relevant Lines:	16181

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💛 - Coveralls