Merge bitcoin/bitcoin#29219: fuzz: Improve fuzzing stability for ellswift_roundtrip harness

154fcce [fuzz] Improve fuzzing stability for ellswift_roundtrip harness (dergoegge)

Pull request description:

  See #29018

ACKs for top commit:
  sipa:
    utACK 154fcce
  brunoerg:
    crACK 154fcce

Tree-SHA512: 1e1ee47467a4a0d3a4e79f672018b440d8b3ccafba7428d37b9d0b8d3afd07e3f64f53ee668ed8a6a9ad1919422b5970814eaf857890acae7546951d8cb141d6

Author: fanquake

src/test/fuzz/key.cpp

@@ -322,7 +322,10 @@ FUZZ_TARGET(ellswift_roundtrip, .init = initialize_key)
     auto encoded_ellswift = key.EllSwiftCreate(ent32);
     auto decoded_pubkey = encoded_ellswift.Decode();
 
-    assert(key.VerifyPubKey(decoded_pubkey));
+    uint256 hash{ConsumeUInt256(fdp)};
+    std::vector<unsigned char> sig;
+    key.Sign(hash, sig);
+    assert(decoded_pubkey.Verify(hash, sig));
 }
 
 FUZZ_TARGET(bip324_ecdh, .init = initialize_key)