TransformerBasedClassification: validations_per_epoch > 2 leaves the model in eval mode

[chschroeder]

Bug description

When TransformerBasedClassification is initialized with validations_per_epoch greater 1, then the model is incorrectly in eval mode in _train_loop_process_batches() (starting with the second iteration).

Steps to reproduce

Set validations_per_epoch to 2 and observe the training loop using the debugger.

Expected behavior

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Environment:

small-text version: 1.3.1
small-text integrations (e.g., transformers): transformers

Addition information

Fixing the functionality is a one liner, the test is most of the effort. Luckily, this setting is 1 by default, so unless you set this purpose, you are likely not affected by this bug.