Install fish shell for CI testing feature

[uilianries]

Related to conan-io/conan-center-index#17719

We need to run Fish shell in Mac and Linux machines to validate the new feature integration.

To install in Ubuntu, we can add their launchpad repo and install directly:

https://launchpad.net/~fish-shell/+archive/ubuntu/release-3

sudo apt-add-repository ppa:fish-shell/release-3
sudo apt update
sudo apt install fish

It's possible to download tar file directly and install, but I didn't check its dependencies.

On Mac, it's available via Brew:

https://formulae.brew.sh/formula/fish

So a simple brew install fish should be enough.

Extra info about the installation: https://github.com/fish-shell/fish-shell?tab=readme-ov-file#getting-fish