exercises(linked-list): test: fix for Zig 0.12.0-dev

[yctai1994]

Fix the following compiler warning when doing the practice in the CLI.

version: zig-v0.12.0-dev.2059+42389cb9c

linked-list/test_linked_list.zig:71:9: error: local variable is never mutated
    var list = List{};
        ^~~~

[github-actions]

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[ee7]

The Zig track currently supports only Zig 0.11.0:

zig/docs/INSTALLATION.md

Lines 6 to 11 in c7a723b

	## Zig version
	Exercism currently supports Zig 0.11.0 (released on 2023-08-04) only.
	An exercise may be compatible with a different Zig version, but that isn't guaranteed.
	Zig has not yet reached version 1.0, and breaking changes are common.

However, I'm happy to improve compatibility with Zig master when it doesn't break support for 0.11.0, so I'll merge this - thanks. I think it was the only test case on the track that didn't support Zig master.

[yctai1994]

The Zig track currently supports only Zig 0.11.0:

Oh, ok, thanks!

I think it was the only test case on the track that didn't support Zig master.

Yeah, it took me a couple of days to sweep all the practices on this track. This is the only one that isn't compatible with the nightly version.