wallet: ensure wallet files are not reused across chains

src/dummywallet.cpp

@@ -50,6 +50,7 @@ void DummyWalletInit::AddWalletOptions(ArgsManager& argsman) const
         "-flushwallet",
         "-privdb",
         "-walletrejectlongchains",
+        "-walletcrosschain",
         "-unsafesqlitesync",
     });
 }