Mark which tests should be skipped for python 3.9

[freddyaboulton]

Pull Request Description

Third time's the charm 😅

Fix broken nightlies by marking tests as being skipped for 3.9.

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After creating the pull request: in order to pass the release_notes_updated check you will need to update the "Future Release" section of docs/source/release_notes.rst to include this pull request by adding :pr:123.

[codecov]

Codecov Report

Merging #3133 (dddd54b) into main (3aa1b36) will decrease coverage by 0.1%.
The diff coverage is 60.0%.

@@           Coverage Diff           @@
##            main   #3133     +/-   ##
=======================================
- Coverage   99.7%   99.7%   -0.0%     
=======================================
  Files        317     317             
  Lines      30711   30718      +7     
=======================================
+ Hits       30607   30610      +3     
- Misses       104     108      +4     

Impacted Files	Coverage Δ
evalml/tests/conftest.py	96.0% <33.4%> (-0.5%)	⬇️
...alml/tests/component_tests/test_arima_regressor.py	100.0% <100.0%> (ø)
...tests/component_tests/test_polynomial_detrender.py	100.0% <100.0%> (ø)
...ml/tests/component_tests/test_prophet_regressor.py	100.0% <100.0%> (ø)
.../tests/pipeline_tests/test_time_series_pipeline.py	99.8% <100.0%> (+0.1%)	⬆️

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[freddyaboulton]

Passing nightlies here:

https://github.com/alteryx/evalml/runs/4459458578?check_suite_focus=true
https://github.com/alteryx/evalml/runs/4459458178?check_suite_focus=true
https://github.com/alteryx/evalml/runs/4459458670?check_suite_focus=true

They are all from this commit ad0aa24

[freddyaboulton]

There's coverage in the passing windows/linux 3.9

[jeremyliweishih]

🙏 thank you