Fix docstring error in IllegalMonthError and remove dead URL in mro.rst

[Jah-yee]

Good day

This PR fixes two documentation issues in python/cpython:

1. IllegalMonthError docstring (calendar.IllegalMonthError docs omit IndexError base class #148663): The docstring incorrectly mentions IndexError but the code raises ValueError. Updated to reflect the actual exception type.

2. Dead URL in mro.rst (A Dead URL in mro.rst doc #148909): Removed a dead URL reference from the mro documentation.

Thank you for your work on this project. I hope this small fix is helpful. Please let me know if there's anything to adjust.

Warmly, RoomWithRoof

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📚 Documentation preview 📚: https://cpython-previews--148924.org.readthedocs.build/

[bedevere-app]

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[StanFromIreland]

IllegalMonthError docstring

The documentation was fixed instead in 435be06, please revert your changes.

[ByteFlowing1337]

Isn’t this URL valid and can be opened? The dead URL mentioned in the issue #148909 seems just because that website does not support TLS, but we can visit it via http.

[StanFromIreland]

I'm sorry but I have to close, neither of the changes are correct. Furthermore, please don't combine two issues into one PR in the future. I suggest you read the devguide, it contains a lot of helpful information on contributing: https://devguide.python.org/