Brush up the GitHub Actions configuration

[garrison]

@mrossinek and I took a pass over the GitHub Actions configuration, which resulted in a few updates.

• update README line about dev & minimum version tests
• propagate the remaining changes that made it into qiskit-addon-utils
• remember to change GitHub pages configuration to use Actions when this is merged (if relevant)

[coveralls]

Pull Request Test Coverage Report for Build 10706138710

Details

• 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 100.0%

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Totals
Change from base Build 10704142559:	0.0%
Covered Lines:	2408
Relevant Lines:	2408

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💛 - Coveralls