CompatHelper: add new compat entry for EarthSciMLBase at version 0.20 for package docs, (keep existing compat)

[github-actions]

This pull request sets the compat entry for the EarthSciMLBase package to 0.20 for package docs.
This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry.
It is your responsibility to make sure that your package tests pass before you merge this pull request.
Note: Consider registering a new release of your package immediately after merging this PR, as downstream packages may depend on this for tests to pass.

[github-actions]

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