Use Python 3.7.5 in CI

[kimadeline]

For #8296

• Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR)
• Title summarizes what is changing
• Has a news entry file (remember to thank yourself!)
• Appropriate comments and documentation strings in the code
• Has sufficient logging.
• Has telemetry for enhancements.
• Unit tests & system/integration tests are added/updated
• Test plan is updated as appropriate
• package-lock.json has been regenerated by running npm install (if dependencies have changed)
• The wiki is updated with any design decisions/details.

[karthiknadig]

Do we need to specify the minor version?

[kimadeline]

Maybe not? Let me try removing it and see if the pipeline fails

[codecov-io]

Codecov Report

Merging #8297 into master will decrease coverage by 0.32%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master   #8297      +/-   ##
=========================================
- Coverage   59.32%     59%   -0.33%     
=========================================
  Files         504     504              
  Lines       23087   23087              
  Branches     3736    3731       -5     
=========================================
- Hits        13697   13622      -75     
- Misses       8498    8573      +75     
  Partials      892     892

Impacted Files	Coverage Δ
src/client/testing/serviceRegistry.ts	48.64% <0%> (-46.85%)	⬇️
src/client/testing/codeLenses/main.ts	44.44% <0%> (-33.34%)	⬇️
...t/datascience/jupyter/jupyterDataRateLimitError.ts	66.66% <0%> (-33.34%)	⬇️
src/client/formatters/serviceRegistry.ts	75% <0%> (-25%)	⬇️
...ience/jupyter/jupyterDebuggerRemoteNotSupported.ts	75% <0%> (-25%)	⬇️
...cience/jupyter/jupyterDebuggerNotInstalledError.ts	60% <0%> (-20%)	⬇️
src/client/common/utils/icons.ts	83.33% <0%> (-16.67%)	⬇️
src/client/api.ts	78.57% <0%> (-14.29%)	⬇️
src/client/datascience/cellFactory.ts	75.86% <0%> (-13.8%)	⬇️
src/client/common/utils/platform.ts	76.47% <0%> (-11.77%)	⬇️
... and 3 more

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