force cargo test to run chain sim tests sequentially #1188

Job	Run time
Contracts (nightly) / Interactor tests	9m 50s
Contracts (nightly) / Test Coverage	5m 39s
Contracts (nightly) / Wasm tests	10m 30s
Contracts (nightly) / Clippy linter check	1m 32s
Contracts (nightly) / Rust tests	3m 25s
	30m 56s

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