sandbox: Ignore not found error in sandbox deletion #913

Job	Run time
tests (vmm/sandbox, --all-features)	3m 21s
checks (vmm/sandbox, --all-features)	4m 53s
tests (vmm/task, --all-features)	2m 29s
checks (vmm/task, --all-features)	3m 47s
tests (shim, --all-features)	2m 28s
checks (shim, --all-features)	3m 51s
tests (quark, --all-features)	2m 20s
checks (quark, --all-features)	4m 0s
tests (runc, --all-features)	2m 26s
checks (runc, --all-features)	4m 12s
tests (wasm, --features=wasmedge, 0.11.2)	3m 4s
checks (wasm, --features=wasmedge, 0.11.2)	4m 16s
tests (wasm, --features=wasmtime)	3m 26s
checks (wasm, --features=wasmtime)	4m 28s
	49m 1s

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