fix: use recommended way of updating Fish shell $PATH

[PauloPhagula]

Akin to #11349 rather than setting $PATH directly this change proposes using the fish_add_path builtin command which is the recommended as documented in the docs

See Fish docs [fishshell.com/docs/current/tutorial.html#path]> (https://fishshell.com/docs/current/tutorial.html#path).

A faster way is to use the fish_add_path function... The advantage is that
you don't have to go mucking around in files: just run this once at the
command line, and it will affect the current session and all future instances
too.

Or you can modify $fish_user_paths yourself, but you should be careful not
to append to it unconditionally in config.fish, or it will grow longer and
longer.

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[Bo98]

Maybe want -P here because of #7215?

Probably don't need the set -q stuff either.

This PR does remove support for old fish prior to 2021 so need to make sure we're ok with that.

[PauloPhagula]

@Bo98 thanks for your comments

Maybe want -P here because of #7215?

Added the flag

Probably don't need the set -q stuff either.

Sounds reasonable, but I'd rather keep the pattern, just in case. But if there's a strong opinion about doing it, I'm game too.

This PR does remove support for old fish prior to 2021 so need to make sure we're ok with that.

True, I think its OK given this has been discussed before in #11349 with maintainer saying that

I think if it works in the latest stable brew install fish that's sufficient.

[Bo98]

Sounds reasonable, but I'd rather keep the pattern, just in case. But if there's a strong opinion about doing it, I'm game too.

Earlier PR also seemed OK with removing it: https://github.com/Homebrew/brew/pull/13175/files

[p-linnane]

Rebased to resolve hanging jobs with the new macOS 14 runner.

[Bo98]

I don't use Fish but seems OK to me if people are OK with the backwards compatiblity question above.

[MikeMcQuaid]

Thanks so much for your first contribution! Without people like you submitting PRs we couldn't run this project. You rock, @PauloPhagula!

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If people have backwards compatibility complaints: let's just revert this on the first complaint.