Pyodide 0.28.0 is now stable

[yeicor]

Description

I believe Pyodide version 0.28.0a3 should be replaced with 0.28.0 and tests updated accordingly.

https://github.com/pyodide/pyodide/releases

Build log

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CI config

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[agriyakhetarpal]

Thanks for the reminder! I have assigned this to myself and started #2487.