fix: free space on GH runner before running nix build #308

Job	Run time
nix-build-book	28s
nix-fmt-check	24s
nix-build (fuel, ubuntu-latest)	45s
nix-build (fuel, macos-latest)	2m 0s
nix-build (fuel, macos-arm)	1s
nix-build (fuel-beta-3, ubuntu-latest)	36s
nix-build (fuel-beta-3, macos-latest)	1m 46s
nix-build (fuel-beta-3, macos-arm)	1s
nix-build (fuel-beta-4, ubuntu-latest)	34s
nix-build (fuel-beta-4, macos-latest)	4m 47s
nix-build (fuel-beta-4, macos-arm)	1s
nix-build (fuel-nightly, ubuntu-latest)	4m 17s
nix-build (fuel-nightly, macos-latest)	2m 17s
nix-build (fuel-nightly, macos-arm)	1s
nix-build (sway-vim, ubuntu-latest)	27s
nix-build (sway-vim, macos-latest)	2m 2s
nix-build (sway-vim, macos-arm)	1s
nix-develop	1s
	20m 29s

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