fix(benchmark): add missing setDKGContract call in DKGBenchmark._setup

All ten tests were reverting with WrongDKGContract(). _setup() finalized
the KeyperSet without calling ks.setDKGContract(address(dkg)), so
_checkDKGContract saw address(0) instead of address(this).

Added ks.setDKGContract(address(dkg)) between setPublisher and setFinalized,
mirroring DKGContractTest.t.sol.

Files changed: test/DKGBenchmark.t.sol

Author: jannikluhn

test/DKGBenchmark.t.sol

@@ -65,6 +65,7 @@ contract DKGBenchmark is Test {
         ks.addMembers(members);
         ks.setThreshold(_threshold(n));
         ks.setPublisher(address(dkg));
+        ks.setDKGContract(address(dkg));
         ks.setFinalized();
 
         vm.prank(dao);