Add `unstable-api` feature flag to `pallet-revive` #11293

Job	Run time
preflight / preflight	39s
preflight / ci-versions	1m 0s
build (polkadot-availability-recovery, availability-recovery-regression-bench)	18m 5s
build (polkadot-availability-distribution, availability-distribution-regression-bench)	5m 3s
build (polkadot-node-core-approval-voting, approval-voting-regression-bench)	22m 23s
build (polkadot-statement-distribution, statement-distribution-regression-bench)	3m 57s
publish-benchmarks	0s
	51m 7s

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