VRF reuse when re-registering pool

I expect the following test to pass, yet it fails:
```
diff --git a/eras/shelley/impl/testlib/Test/Cardano/Ledger/Shelley/Imp/PoolSpec.hs b/eras/shelley/impl/testlib/Test/Cardano/Ledger/Shelley/Imp/PoolSpec.hs
index 6b6a48c166..47b54b57b5 100644
--- a/eras/shelley/impl/testlib/Test/Cardano/Ledger/Shelley/Imp/PoolSpec.hs
+++ b/eras/shelley/impl/testlib/Test/Cardano/Ledger/Shelley/Imp/PoolSpec.hs
@@ -180,6 +180,15 @@ spec = describe "POOL" $ do
expectPool kh (Just vrf)
expectFuturePool kh Nothing

+ it "re-register a pool with its own future VRF" $ do
+ (kh, vrf) <- registerNewPool
+ newVrf <- freshKeyHashVRF
+ tx <- registerPoolTx <$> poolParams kh newVrf
+ submitTx_ tx
+ expectPool kh (Just vrf)
+ expectFuturePool kh (Just newVrf)
+ submitTx_ tx
+
it "re-register a pool with a fresh VRF" $ do
(kh, vrf) <- registerNewPool
vrfNew <- freshKeyHashVRF
```