readthedocs fix after Github Actions transition

[bernardopacini]

Purpose

This fixes the readthedocs yaml file after it broke when switching from Travis to GH Actions.

Type of change

Maintenance Select the appropriate type(s) that describe this PR

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (non-backwards-compatible fix or feature)
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Documentation update X Other (please describe)

[coveralls]

Pull Request Test Coverage Report for Build 611609713

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 87.491%

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Totals
Change from base Build 593052013:	0.0%
Covered Lines:	3728
Relevant Lines:	4261

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💛 - Coveralls

[bernardopacini]

Closing this PR as RTD was not set to trigger for it.