Bump one CI config to ubuntu-24.04

[bjodah]

ubuntu-20.04 no longer available on github actions

[bjodah]

@lkeegan I'm trying to mirror your changes in symengine/symengine#2104, and I'm a bit at loss when it comes to how conda is configured. If it's not too much trouble for you I'd really appreciate if you could take a look when you find the time!

[lkeegan]

@bjodah github appends --noprofile --norc by default to the bash command which prevents conda from activating so we need to explicitly declare a bash command that doesn't do this 6b920b6 (see https://github.com/conda-incubator/setup-miniconda?tab=readme-ov-file#important)

[bjodah]

I see, I missed that part, thank you for pointing that out.

[bjodah]

Let's address AppVeyor in a separate PR. Thank you @lkeegan for your help.