Fixed WandbLogger save_dir is not set after creation (#12748)

[tshu-w]

What does this PR do?

Fixes #12748 make sure WandbLogger save_dir set after creation.

Does your PR introduce any breaking changes? If yes, please list them.

No.

Test

from pytorch_lightning.cli import LightningCLI

from pytorch_lightning.demos.boring_classes import DemoModel, BoringDataModule

class LitCLI(LightningCLI):
    def before_instantiate_classes(self) -> None:
        print(self.config[self.subcommand].trainer.logger)

def run():
    cli = LitCLI(
        DemoModel,
        BoringDataModule,
        trainer_defaults={"max_epochs": 2},
        save_config_callback=False,
    )


if __name__ == "__main__":
    run()

python cli.py fit --trainer.logger WandbLogger

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