config: enable NeoXDKG fork on testnet

Ref.
#427 (comment).

Close #427.

Signed-off-by: Anna Shaleva <[email protected]>

Author: AnnaShaleva

config/genesis_testnet.json

@@ -15,6 +15,7 @@
     "arrowGlacierBlock": 0,
     "grayGlacierBlock": 0,
     "shanghaiTime": 0,
+    "neoXDKGBlock": 1990080,
     "dbft": {
       "period": 5,
       "standbyValidators": [