scripted-diff: Replace EnsureChainman with Assert in unit tests

-BEGIN VERIFY SCRIPT-
sed --regexp-extended -i -e 's/EnsureChainman\((m?_?node)\)\./Assert(\1.chainman)->/g' $(git grep -l EnsureChainman)
-END VERIFY SCRIPT-

src/test/util/mining.cpp

@@ -32,7 +32,7 @@ CTxIn MineBlock(const NodeContext& node, const CScript& coinbase_scriptPubKey)
         assert(block->nNonce);
     }
 
-    bool processed{EnsureChainman(node).ProcessNewBlock(Params(), block, true, nullptr)};
+    bool processed{Assert(node.chainman)->ProcessNewBlock(Params(), block, true, nullptr)};
     assert(processed);
 
     return CTxIn{block->vtx[0]->GetHash(), 0};