mlflow: Handle race in create experiment

[garymm]

Fixes: https://github.com/Astera-org/obelisk/issues/805
Change-Id: I196f285a77a931b967ea9cfa49294d8e45e82c2a

[codecov]

Codecov Report

Attention: Patch coverage is 94.28571% with 2 lines in your changes missing coverage. Please review.

Project coverage is 93.47%. Comparing base (c514376) to head (305a7ff).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
..._loop_utils/metric_writers/mlflow/metric_writer.py	83.33%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #17   +/-   ##
=======================================
  Coverage   93.47%   93.47%           
=======================================
  Files          42       42           
  Lines        2559     2591   +32     
=======================================
+ Hits         2392     2422   +30     
- Misses        167      169    +2     

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