rococo_contracts: Adds missing migration (#4112)

Co-authored-by: Liam Aharon <[email protected]>

cumulus/parachains/runtimes/contracts/contracts-rococo/src/contracts.rs

@@ -71,7 +71,7 @@ impl Config for Runtime {
 	type MaxDebugBufferLen = ConstU32<{ 2 * 1024 * 1024 }>;
 	type MaxDelegateDependencies = ConstU32<32>;
 	type CodeHashLockupDepositPercent = CodeHashLockupDepositPercent;
-	type Migrations = ();
+	type Migrations = (pallet_contracts::migration::v16::Migration<Runtime>,);
 	type RuntimeHoldReason = RuntimeHoldReason;
 	type Debug = ();
 	type Environment = ();