Fixed setting of _save_dir when run initiated externally

[THasthika]

What does this PR do?

It moves the setting of the _save_dir of WandbLogger from the clause where it only runs when the experiment is set to None.

With this change we can set the experiment externally and have the models be uploaded to the wandb servers.

Fixes #7103

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[codecov]

Codecov Report

Merging #7106 (3ea0582) into master (f48ac62) will decrease coverage by 5%.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master   #7106    +/-   ##
=======================================
- Coverage      92%     87%    -5%     
=======================================
  Files         197     197            
  Lines       12622   12622            
=======================================
- Hits        11611   11004   -607     
- Misses       1011    1618   +607     

[awaelchli]

Could you add/modify the tests in tests/loggers/test_wandb.py or show us a reproducible example so we can help do that. Thanks for sending a fix <3

[THasthika]

Could you add/modify the tests in tests/loggers/test_wandb.py or show us a reproducible example so we can help do that. Thanks for sending a fix <3

I've added a single test to check if the save_dir is set in the logger when experiment is set manually. The test is in the test_wandb_logger_init function in tests/loggers/test_wandb.py. Will that be alright?

[awaelchli]

Well done

[tchaton]

LGTM ! Nice