Add `fast-runtime` feature to chain-spec-generator (#196) #6

Job	Run time
Extract tasks from matrix	9s
check-migrations (polkadot, polkadot-runtime, relay/polkadot, wss://polkadot-try-runtime-node.par...	19m 34s
check-migrations (kusama, staging-kusama-runtime, relay/kusama, wss://kusama-try-runtime-node.par...	13m 43s
check-migrations (asset-hub-kusama, asset-hub-kusama-runtime, system-parachains/asset-hubs/asset-...	7m 29s
check-migrations (asset-hub-polkadot, asset-hub-polkadot-runtime, system-parachains/asset-hubs/as...	6m 49s
check-migrations (bridge-hub-kusama, bridge-hub-kusama-runtime, system-parachains/bridge-hubs/bri...	5m 58s
check-migrations (bridge-hub-polkadot, bridge-hub-polkadot-runtime, system-parachains/bridge-hubs...	5m 50s
check-migrations (collectives-polkadot, collectives-polkadot-runtime, system-parachains/collectiv...	6m 6s
check-migrations (encointer-kusama, encointer-kusama-runtime, system-parachains/encointer, wss://...	4m 29s
	1h 10m 7s

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