meson: add gio-unix-2.0 dependency
On some platforms, it is not propagated by gtk+-3.0 so we need to declare it explicitly. It is a good practice anyway.
Downstream issue: https://github.com/NixOS/nixpkgs/issues/36468
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On some platforms, it is not propagated by gtk+-3.0 so we need to declare it explicitly. It is a good practice anyway.
Downstream issue: https://github.com/NixOS/nixpkgs/issues/36468