Add typing for trainer.logger

[carmocca]

What does this PR do?

This uncovered a bug with track_grad_norm where it fails with logger=False

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

None

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• [n/a] Did you write any new necessary tests? (not for typos and docs)
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cc @awaelchli @edward-io @Borda @ananthsub

[github-actions]

Build Error! No Linked Issue found. Please link an issue or mention it in the body using #<issue_id>

[tchaton]

LGTM !