Fixes wrong epoch count in trainer under some conditions

[i3hz]

What does this PR do?

When using an iterable dataset, the Trainer incorrectly calculates steps_in_epoch as max_steps,
causing epoch values to be 2x smaller than expected.

Fixes #41913

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• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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  to it if that's the case. epoch in the log message uses a wrong denominator under some conditions #41913
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• Did you write any new necessary tests?

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