Fix flaky keras test

[harupy]

What changes are proposed in this pull request?

test_model_save_load in test_keras_model_export.py fails when the gradients of a model explode during training and the prediction values become infinity. This PR aims to fix this issue by using a smaller learning rate.

https://github.com/mlflow/mlflow/pull/2914/checks?check_run_id=762832699#step:5:347

How is this patch tested?

(Details)

Release Notes

Is this a user-facing change?

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• Yes. Give a description of this change to be included in the release notes for MLflow users.

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What component(s), interfaces, languages, and integrations does this PR affect?

Components

• area/artifacts: Artifact stores and artifact logging
• area/build: Build and test infrastructure for MLflow
• area/docs: MLflow documentation pages
• area/examples: Example code
• area/model-registry: Model Registry service, APIs, and the fluent client calls for
  Model Registry
• area/models: MLmodel format, model serialization/deserialization, flavors
• area/projects: MLproject format, project running backends
• area/scoring: Local serving, model deployment tools, spark UDFs
• area/tracking: Tracking Service, tracking client APIs, autologging

Interface

• area/uiux: Front-end, user experience, JavaScript, plotting
• area/docker: Docker use across MLflow's components, such as MLflow Projects and MLflow Models
• area/sqlalchemy: Use of SQLAlchemy in the Tracking Service or Model Registry
• area/windows: Windows support

Language

• language/r: R APIs and clients
• language/java: Java APIs and clients

Integrations

• integrations/azure: Azure and Azure ML integrations
• integrations/sagemaker: SageMaker integrations

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• rn/breaking-change - The PR will be mentioned in the "Breaking Changes" section
• rn/none - No description will be included. The PR will be mentioned only by the PR number in the "Small Bugfixes and Documentation Updates" section
• rn/feature - A new user-facing feature worth mentioning in the release notes
• rn/bug-fix - A user-facing bug fix worth mentioning in the release notes
• rn/documentation - A user-facing documentation change worth mentioning in the release notes

[codecov-commenter]

Codecov Report

Merging #2926 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2926   +/-   ##
=======================================
  Coverage   85.04%   85.04%           
=======================================
  Files          20       20           
  Lines        1050     1050           
=======================================
  Hits          893      893           
  Misses        157      157           

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[harupy]

I wrote a notebook to verify that a small learning rate prevents gradients from exploding.

https://colab.research.google.com/drive/1a0b60Gk9ItEfQDluyi8W49xE6Uckf5eS?usp=sharing

[aarondav]

Looks OK. I wonder if we could also set a fixed random seed so this is deterministic?

[harupy]

@aarondav We could do that too. I'll add a fixture that fixes a random seed.