Fix v_num formatting for RichProgressBar

[SkafteNicki]

What does this PR do?

Fixes #20268
Minor consistency issue. For RichProgressBar the v_num experiment indicator is currently showing up as 0.000, 1.000 etc. due this being interpret as a metric and then the default metric formatting is applied

pytorch-lightning/src/lightning/pytorch/callbacks/progress/rich_progress.py

Line 219 in 791753b

metrics_format: str = ".3f"

PR makes the change that the format is only applied to floats and not ints, which would fix this.
This somewhat is consistent with the TQDM progress bar which also includes int from formatting (padding)

pytorch-lightning/src/lightning/pytorch/callbacks/progress/tqdm_progress.py

Line 49 in 791753b

should_be_padded = isinstance(n, (float, str))

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📚 Documentation preview 📚: https://pytorch-lightning--21040.org.readthedocs.build/en/21040/