Fix LightningCLI not saving correctly seed_everything for run=True

[mauvilsa]

What does this PR do?

Fixes a bug in LightningCLI where the saved config does not save the actual value used for seed_everything. The intention of the saved config is reproducibility, and by not having the correct seed_everything, it is not possible to reproduce. The bug only affects run=True and seed_everything=True (the default).

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[carmocca]

Nice catch!