chore(deps): update cachix/cachix-action action to v15 #659

Job	Run time
nix (aarch64, fmt -- --check)	33s
nix (aarch64, eval .#apps.$_system.nixos-shell.program)	36s
nix (aarch64, eval .#apps.$_system.setup.program)	16s
nix (x86_64, fmt -- --check)	2m 56s
nix (x86_64, eval .#apps.$_system.nixos-shell.program)	3m 57s
nix (x86_64, eval .#apps.$_system.setup.program)	2m 52s
nix (develop .#jdk8 --profile result, x86_64)	4m 5s
nix (develop .#jdk11 --profile result, x86_64)	4m 45s
nix (develop .#jdk17 --profile result, x86_64)	3m 2s
nix (develop .#php74 --profile result, x86_64)	2m 42s
nix (develop .#php74-composer1 --profile result, x86_64)	3m 59s
nix (develop .#php80 --profile result, x86_64)	4m 15s
nix (develop .#php81 --profile result, x86_64)	3m 46s
nix (build .#homeConfigurations."tobias@gamer".activationPackage, x86_64)	3m 24s
nix (build .#nixOnDroidConfigurations.pixel7a.activationPackage --impure, aarch64)	32s
nix (build .#nixosConfigurations.argon.config.system.build.toplevel, aarch64, argon)	1m 48s
nix (build .#nixosConfigurations.krypton.config.system.build.toplevel, x86_64, krypton)	4m 33s
nix (build .#nixosConfigurations.neon.config.system.build.toplevel, x86_64, neon, --async)	9m 10s
nix (build .#nixosConfigurations.xenon.config.system.build.toplevel, aarch64, xenon)	3m 15s
nix (build .#packages.$_system.rpi-firmware, aarch64)	10s
nix (build .#packages.$_system.rpi-image, aarch64)	3m 17s
nix (build .#packages.$_system.installer-image, x86_64)	5m 16s
	1h 9m 9s

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