Fix scale_batch_size() when using a LRScheduler

[HansBambel]

The order of the learning rate updates when run_training_teardown() was pending was restricting the use of a learning rate scheduler monitoring a metric that only exists at the end of a validation loop.

Due to @SkafteNicki's suggestion I changed the order of the self.update_learning_rates() and self.run_training_teardown() in the training_loop.py.

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What does this PR do?

Fixes #1889

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